Filed Pursuant to Rule 424(b)(2)
Registration No. 333-209714

CALCULATION OF REGISTRATION FEE

PROSPECTUS SUPPLEMENT

(To Prospectus dated February 25, 2016)

$375,000,000

AVISTA CORPORATION

First Mortgage Bonds, 4.35% Series due 2048

Our First Mortgage Bonds, 4.35% Series due 2048 (the “Offered Bonds”), constitute a series of our Bonds described in the accompanying prospectus.

We will pay interest on the Offered Bonds semiannually in arrears on June 1 and December 1 of each year. The first such payment will be made on December 1, 2018. The Offered Bonds will mature on June 1, 2048, unless redeemed on an earlier date. The Offered Bonds are redeemable at our option, in whole at any time or in part from time to time, at the applicable redemption prices as described herein. See “Description of the Offered Bonds”.

The Offered Bonds will be secured equally with all other bonds outstanding under our Mortgage (as defined in the accompanying prospectus).

See “Risk Factors” on page S-3 for reference to certain factors you should consider before buying the Offered Bonds.

Neither the Securities and Exchange Commission nor any other regulatory body has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus supplement or the accompanying prospectus. Any representation to the contrary is a criminal offense.

The initial public offering price set forth above does not include accrued interest, if any. Interest on the Offered Bonds will accrue from May 22, 2018 and must be paid by the purchasers if the Offered Bonds are delivered after May 22, 2018.

The underwriters expect to deliver the Offered Bonds to the purchasers through the facilities of The Depository Trust Company against payment in New York, New York on May 22, 2018.

Joint Book-Running Managers

Co-Managers

The date of this prospectus supplement is May 15, 2018

TABLE OF CONTENTS

Prospectus Supplement

Prospectus

In making your investment decision, you should rely only on the information included or incorporated by reference in this prospectus supplement, the accompanying prospectus and any free writing prospectus we may authorize to be delivered to you. We have not authorized anyone to provide you with any other information. You should assume that the information contained or incorporated in this prospectus supplement and the accompanying prospectus is accurate only as of the respective dates of these documents. We are not offering to sell these securities and we are not soliciting offers to buy these securities in any jurisdiction in which offers or sales are not permitted.

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RISK FACTORS

General

Investing in the Offered Bonds involves risk. You should review all the information contained or incorporated by reference in this prospectus supplement and the accompanying prospectus before deciding to invest. See “Where You Can Find More Information” in the accompanying prospectus. In particular, you should carefully consider the risks and uncertainties discussed in “Risk Factors”, “Forward-Looking Statements” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” in our annual report on Form 10-K and quarterly report on Form 10-Q filed with the Securities and Exchange Commission (the “SEC”) and incorporated herein by reference.

In addition to the risks and uncertainties referred to above, there are certain risks associated with the Offered Bonds as described below.

Risks Related to an Investment in the Offered Bonds

We cannot assure you that an active trading market for the Offered Bonds will develop.

The Offered Bonds constitute a new issue of securities with no established trading market. We do not intend to apply for listing of the Offered Bonds on any securities exchange or automated quotation system. There can be no assurance as to the liquidity of any market that may develop for the Offered Bonds, the ability of the bondholders to sell their Offered Bonds or the price at which the bondholders will be able to sell the Offered Bonds. Future trading prices of the Offered Bonds will depend on many factors including, among other things, prevailing interest rates, our operating results and the market for similar securities.

SAFE HARBOR FOR FORWARD-LOOKING STATEMENTS

From time to time, we make forward-looking statements such as statements regarding projected or future financial performance, cash flows, capital expenditures, dividends, capital structure, other financial items, strategic goals and objectives, and plans for operations. These statements are based upon underlying assumptions (many of which are based, in turn, upon further assumptions). These statements are made both in our reports filed under the Securities Exchange Act of 1934, as amended, and elsewhere. Forward-looking statements are all statements except those of historical fact, including, without limitation, those that are identified by the use of words such as, but not limited to, “will”, “may”, “could”, “should”, “intends”, “plans”, “seeks”, “anticipates”, “estimates”, “expects”, “forecasts”, “projects”, “predicts”, and similar expressions.

Forward-looking statements are subject to a variety of risks and uncertainties and other factors. Most of these factors are beyond our control, and many of them could have a significant effect on our operations, results of operations, financial condition or cash flows. This could cause actual results to differ materially from those anticipated in our forward-looking statements. Such risks, uncertainties and other factors include, among others, those listed or referred to under the caption “Risk Factors” in this prospectus supplement, the accompanying prospectus and the documents incorporated herein by reference.

Our expectations, beliefs and projections are expressed in good faith. We believe they are reasonable based on, among other considerations, an examination of historical operating trends, data contained in our records and other data available from third parties. However, there can be no assurance that our expectations, beliefs or projections will be achieved or accomplished. Furthermore, any forward-looking statement speaks only as of the date on which such statement is made. We undertake no obligation to update any forward-looking statement or statements to reflect events or circumstances that occur after the date on which such statement is made or to reflect the occurrence of unanticipated events, except as required by law. New risks, uncertainties and other factors emerge from time to time, and it is not possible for us to predict all such factors, nor can we assess the effect of each such factor on our business or the extent that any such factor or combination of factors may cause actual results to differ materially from those contained in any forward-looking statement.

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THE COMPANY

Avista is primarily an electric and natural gas utility, with certain other business ventures. Our corporate headquarters are in Spokane, Washington. Our utility operations provide electricity and natural gas in parts of the Pacific Northwest, and, through a subsidiary, in the City and Borough of Juneau, Alaska. For more information, see the accompanying prospectus and the documents incorporated herein by reference.

USE OF PROCEEDS

We estimate that the proceeds from this offering will be approximately $370.8 million, after deducting the underwriting discount and estimated offering expenses payable by us.

We will use the net proceeds from the sale of the Offered Bonds:

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SELECTED FINANCIAL INFORMATION

Set forth below is certain selected consolidated financial information for the years ended December 31, 2015, 2016 and 2017 and the three months ended March 31, 2017 and 2018. This financial information has been selected from the consolidated financial statements of Avista, which are incorporated herein by reference. This information should be read in conjunction with our consolidated financial statements and related notes, management’s discussion and analysis of results of operations and other financial information, which are incorporated by reference herein.

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DESCRIPTION OF THE OFFERED BONDS

The following description of the particular terms of the Offered Bonds supplements the description of the general terms and provisions of the Bonds set forth under “Description of the Bonds” in the accompanying prospectus, to which description reference is hereby made. Certain capitalized terms used and not defined in this prospectus supplement are defined under “Description of the Bonds” in the accompanying prospectus.

General

The Offered Bonds will be issued as one series of bonds under our Mortgage, which is more fully described in the accompanying prospectus.

The Offered Bonds will be issued in fully registered form only, without coupons. The Offered Bonds will be initially represented by one or more fully registered global securities (the “Global Securities”) deposited with or on behalf of The Depository Trust Company (“DTC”), as depositary, and registered in the name of DTC or DTC’s nominee. A beneficial interest in a Global Security will be shown on, and transfers or exchanges thereof will be effected only through, records maintained by DTC and its participants, as described below under “— Book-Entry Only Issuance — The Depository Trust Company”. The authorized denominations of the Offered Bonds will be $1,000 and any larger amount that is an integral multiple of $1,000. Except in the limited circumstances described below, the Offered Bonds will not be exchangeable for Offered Bonds in definitive certificated form.

Principal, Maturity and Interest

We are issuing $375,000,000 aggregate principal amount of Offered Bonds. The Offered Bonds will mature on June 1, 2048. We may, without the consent of holders of the Offered Bonds, issue additional bonds of the same series having the same interest rate, maturity and other terms as the Offered Bonds. Such additional bonds may be offered at the same or any different price.

Interest on the Offered Bonds will accrue at the rate of 4.35% per annum and will be payable semi-annually in arrears on June 1 and December 1 of each year (each such date, an “Interest Payment Date”), and at maturity. The first such payment will be made on December 1, 2018. We will make each interest payment to the holders of record on the immediately preceding May 15 and November 15.

Interest on the Offered Bonds will accrue from the date of original issuance or, if interest has already been paid, from the date it was most recently paid. Interest will be computed on the basis of a 360-day year comprised of twelve 30-day months.

Optional Redemption

Prior to the Par Call Date, the Offered Bonds will be redeemable in whole at any time, or in part from time to time, at the option of Avista, at a redemption price equal to the greater of:

plus, in either of the above cases, accrued and unpaid interest on such Offered Bonds to the redemption date.

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On or after the Par Call Date, the Offered Bonds will be redeemable in whole at any time, or in part from time to time, at the option of Avista at a redemption price equal to 100% of the principal amount of the Offered Bonds being redeemed plus accrued and unpaid interest on such Offered Bonds to the date of redemption.

“Par Call Date” means December 1, 2047 (the date that is six months prior to the stated maturity date).

“Treasury Yield” means, with respect to any redemption of Offered Bonds:

The Treasury Yield shall be rounded to two decimal places. The Treasury Yield shall be calculated as of the third business day preceding the earlier of (x) the date notice of redemption is mailed to holders of the Offered Bonds and (y) the date irrevocable arrangements with the Trustee for the mailing of such notice shall have been made, as the case may be (the “Calculation Date”).

“Statistical Release” means the daily statistical release entitled “H.15 Selected Interest Rates”, or any successor publication, published by the Board of Governors of the Federal Reserve System, or any successor entity; or, if such Board of Governors no longer publishes the information contained in such statistical release, a publication containing similar information published by the U.S. Department of the Treasury, or any successor or other U.S. governmental body.

If less than all the outstanding Offered Bonds are to be redeemed, the particular Bonds to be redeemed will be selected by the Trustee by such method of random selection as the Trustee shall deem fair and appropriate; provided, however, that if the Company shall have offered to purchase all the Offered Bonds then outstanding and less than all of such Bonds have been tendered to the Company for such purchase, the Trustee, if so directed by the Company, will select for redemption all such Bonds that have not been so tendered. So long as a securities depositary is the only registered owner of the Offered Bonds, beneficial interests Bonds will be selected in accordance with the applicable procedures of such depositary. See “Book-Entry Only Issuance — The Depository Trust Company”.

Book-Entry Only Issuance — The Depository Trust Company

DTC will act as initial securities depositary for the Offered Bonds. The Offered Bonds will be issued only as fully-registered securities registered in the name of Cede & Co. (DTC’s nominee) or such other name as may be requested by an authorized representative of DTC. One or more fully-registered global certificates will be issued, representing in the aggregate the total principal amount of the Offered Bonds, and will be deposited with DTC or a custodian therefor.

The following is based upon information furnished by DTC:

DTC is a limited-purpose trust company organized under the New York Banking Law, a “banking organization” within the meaning of the New York Banking Law, a member of the Federal Reserve System, a “clearing corporation” within the meaning of the New York Uniform Commercial Code, and a “clearing

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agency” registered pursuant to the provisions of Section 17A of the Securities Exchange Act of 1934, as amended. DTC holds and provides asset servicing for issues of U.S. and non-U.S. equity issues, corporate and municipal debt issues and money market instruments that its participants (“Direct Participants”) deposit with DTC. DTC also facilitates the post-trade settlement among Direct Participants of sales and other securities transactions in deposited securities through electronic computerized book-entry transfers and pledges between Direct Participants’ accounts. This eliminates the need for physical movement of securities certificates.

Direct Participants include both U.S. and non-U.S. securities brokers and dealers, banks, trust companies, clearing corporations, and certain other organizations. DTC is a wholly-owned subsidiary of The Depository Trust & Clearing Corporation (“DTCC”). DTCC is the holding company for DTC, National Securities Clearing Corporation and Fixed Income Clearing Corporation, all of which are registered clearing agencies.

DTCC is owned by the users of its regulated subsidiaries. Access to the DTC system is also available to others such as both U.S. and non-U.S. securities brokers and dealers, banks, trust companies, and clearing corporations that clear through or maintain a custodial relationship with a Direct Participant, either directly or indirectly (“Indirect Participants” and, together with Direct Participants, “Participants”). The DTC Rules applicable to its Participants are on file with the Securities and Exchange Commission. More information about DTC can be found at www.dtcc.com and www.dtc.org. The contents of such websites do not constitute a part of this prospectus supplement.

Purchases of Offered Bonds under the DTC system must be made by or through Direct Participants, which will receive a credit for the Offered Bonds on DTC’s records. The ownership interest of each actual purchaser of each Offered Bond (“Beneficial Owner”) is in turn to be recorded on the Participants’ records. Beneficial Owners will not receive written confirmation from DTC of their purchases. Beneficial Owners, however, are expected to receive written confirmation providing details of the transactions, as well as periodic statements of their holdings, from the respective Participants through which the Beneficial Owners entered into the transactions. Transfers of ownership interests in the Offered Bonds are to be accomplished by entries made on the books of Participants acting on behalf of Beneficial Owners. Beneficial Owners will not receive certificates representing their ownership interests in the Offered Bonds, except in the event that use of the book-entry system for the Offered Bonds is discontinued.

To facilitate subsequent transfers, all Offered Bonds deposited by Direct Participants with DTC are registered in the name of DTC’s partnership nominee, Cede & Co., or such other name as may be requested by an authorized representative of DTC. The deposit of Offered Bonds with DTC and their registration in the name of Cede & Co. or such other DTC nominee do not effect any changes in beneficial ownership. DTC has no knowledge of the actual Beneficial Owners of the Offered Bonds; DTC’s records reflect only the identity of the Direct Participants to whose accounts such Offered Bonds are credited, which may or may not be the Beneficial Owners. The Participants will remain responsible for keeping account of their holdings on behalf of their customers.

Notices and other communications by DTC to Direct Participants, by Direct Participants to Indirect Participants, and by Participants to Beneficial Owners will be governed by arrangements among them, subject to any statutory or regulatory requirements as may be in effect from time to time.

We will send redemption notices to DTC, as the registered owner of the Offered Bonds. If less than all of the Offered Bonds are being redeemed, DTC’s practice is to determine by lot the amount of the interest of each Direct Participant to be redeemed.

Neither DTC nor Cede & Co. (nor any other DTC nominee) will consent or vote with respect to Offered Bonds unless authorized by a Direct Participant in accordance with DTC’s procedures. Under its

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usual procedures, DTC mails an Omnibus Proxy to us as soon as possible after the record date. The Omnibus Proxy assigns Cede & Co.’s consenting or voting rights to those Direct Participants to whose accounts the Offered Bonds are credited on the record date (identified in a listing attached to the Omnibus Proxy).

Payments on the Offered Bonds will be made to Cede & Co. or such other nominee as may be requested by an authorized representative of DTC. DTC’s practice is to credit Direct Participants’ accounts upon DTC’s receipt of funds and corresponding detail information from us or the Mortgage Trustee on the relevant payment date in accordance with their respective holdings shown on DTC’s records. Payments by Participants to Beneficial Owners will be governed by standing instructions and customary practices, as is the case with securities held for the accounts of customers in bearer form or registered in “street name”, and will be the responsibility of such Participants and not of DTC, the Mortgage Trustee or us, subject to any statutory or regulatory requirements as may be in effect from time to time. Payment to Cede & Co. (or such other nominee as may be requested by an authorized representative of DTC) is our responsibility, disbursement of payments to Direct Participants is the responsibility of DTC, and disbursement of payments to the Beneficial Owners is the responsibility of the Participants.

DTC may discontinue providing its services as depositary for the Offered Bonds at any time by giving reasonable notice to us. Under such circumstances, in the event that a successor depositary is not obtained, certificates for the Offered Bonds will be printed and delivered to or upon the order of DTC for redelivering to Participants or Beneficial Owners. Additionally, we may decide to discontinue use of the system of book-entry-only transfers through DTC (or a successor securities depositary) with respect to the Offered Bonds. In that event, certificates for the Offered Bonds will be printed and delivered to or upon the order of DTC for redelivering to Participants or Beneficial Owners.

The information in this section concerning DTC and DTC’s book-entry system is based upon information provided by DTC, and neither we nor the underwriters take any responsibility for the accuracy thereof. Neither we, the Mortgage Trustee nor the underwriters will have any responsibility or liability for any aspect of the records relating to or payments made on account of beneficial ownership interests in the Offered Bonds or for maintaining, supervising or reviewing any such records.

Except as provided herein, a Beneficial Owner of an interest in a global Offered Bond certificate may not receive physical delivery of the Offered Bonds. Accordingly, each Beneficial Owner must rely on the procedures of DTC to exercise any rights in respect of the Offered Bonds.

Miscellaneous

At March 31, 2018, $2,111.7 million of Mortgage Securities were outstanding. This amount includes $483.7 million of nontransferable Mortgage Securities which were issued in order to provide the benefit of the lien of the Mortgage to secure other of our debt obligations (of which we hold $83.7 million). See “Description of the Bonds — Issuance of Additional Mortgage Securities” in the accompanying prospectus and “Liquidity and Capital Resources — Capital Resources — Limitations on Issuances of Preferred Stock and First Mortgage Bonds” in Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations in Avista’s Annual Report on Form 10-K for the year ended December 31, 2017. The Company currently intends to issue the Offered Bonds on the basis of property additions.

The paragraph under the heading “Modification — Modification With Consent” in “Description of the Bonds” in the accompanying prospectus is replaced in its entirety by the following:

In general, the Mortgage, the rights and obligations of Avista and the rights of the Holders may be modified with the consent of 60% in principal amount of the Mortgage Securities outstanding, considered as one class (or, if such modification shall directly affect the Holders of one or more, but less than all, series

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then outstanding, then the consent only of the Holders of 60% in principal amount of the bonds of the series so directly affected then outstanding, considered as one class). However, no modification of the terms of payment of principal or interest, and no modification affecting the lien or reducing the percentage required for modification, is effective against any Holder without its consent. (Original Mortgage, Art. XVIII, Sec. 149; First Supplemental Indenture, Sec. 10; Twenty-ninth Supplemental Indenture, Article II, Section  1).

UNDERWRITING

General

BNY Mellon Capital Markets, LLC, J.P. Morgan Securities LLC, MUFG Securities Americas Inc., and Wells Fargo Securities, LLC are the joint book-running managers of this offering and are the representatives of the underwriters named below (the “Representatives”). We and the Representatives, on behalf of themselves and the other underwriters, have entered into an underwriting agreement with respect to the Offered Bonds. Subject to certain conditions, each underwriter has severally, but not jointly, agreed to purchase the principal amount of Offered Bonds indicated in the following table.

In the underwriting agreement, the underwriters have agreed, subject to the terms and conditions set forth therein, to purchase all of the Offered Bonds if any of the Offered Bonds are purchased. The obligations of the underwriters, including their agreement to purchase the Offered Bonds from us, are several and not joint. The underwriting agreement provides that the obligations of the underwriters pursuant thereto are subject to certain conditions and to approval of legal matters by counsel. The offering of the Offered Bonds by the underwriters is subject to the receipt and acceptance of, and subject to the underwriters’ right to reject, any order in whole or in part.

The underwriters have advised us that they propose to initially offer the Offered Bonds at the public offering price set forth on the cover page of this prospectus supplement and to dealers at that price less a concession not in excess of 0.500% of the principal amount thereof. The underwriters may allow, and the dealers may reallow, a discount not in excess of 0.350% of the principal amount thereof. After the initial offering, the underwriters may change the public offering price and concession.

The underwriting agreement provides for the underwriters to purchase the Offered Bonds from us at discount from the initial public offering price, as shown in the table on the cover page of this prospectus supplement. We estimate that our share of the total expenses of this offering, excluding such underwriting discount, will be approximately $500,000.

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The Offered Bonds are a new issue of securities with no established trading market. We do not intend to apply for listing of the Offered Bonds on any national securities exchange or for inclusion of the Offered Bonds on any automated dealer quotation system. We have been advised by the underwriters that they presently intend to make a market in the Offered Bonds after completion of the offering. However, they are under no obligation to do so and may discontinue any market-making activities at any time without any notice. We cannot assure the liquidity of the trading market for the Offered Bonds or that an active public market for the Offered Bonds will develop. If an active public trading market for the Offered Bonds does not develop, the market price and liquidity of the Offered Bonds may be adversely affected. If the Offered Bonds are traded, they may trade at a discount from their initial offering price, depending on prevailing interest rates, the market for similar securities, our performance and other factors.

In connection with the offering, the Representatives are permitted to engage in transactions that stabilize the market price of the Offered Bonds. Such transactions consist of bids or purchases in the open market to peg, fix or maintain the price of the Offered Bonds.

The Representatives also may impose a penalty bid. This occurs when a particular underwriter repays to the underwriters a portion of the underwriting discount that it has received because the Representatives have repurchased Offered Bonds sold by or for the account of such underwriter in stabilizing or short covering transactions. Any of these activities may stabilize or maintain the market price for the Offered Bonds above independent market levels. The Representatives are not required to engage in these activities and may end any of these activities at any time without notice.

We have agreed to indemnify the several underwriters against certain liabilities, including liabilities under the Securities Act of 1933, as amended, or contribute to payments that the underwriters may be required to make in respect of those liabilities.

Certain of the underwriters and their respective affiliates have, from time to time, performed and may in the future perform, various financial advisory, lending and investment and commercial banking services for us, for which they received or will receive customary fees and expenses. Certain of the underwriters in this offering or their affiliates are lenders under our $400 million credit facility. As described in “Use of Proceeds,” we plan to use a portion of the net proceeds from the issuance of the Offered Bonds to repay borrowings of approximately $39.5 million under this credit facility. As such, certain of the underwriters in this offering or their affiliates will receive a portion of the net proceeds from this offering.

T+5 Settlement Cycle

We expect that delivery of the Offered Bonds will be made against payment therefor on or about May 22, 2018, which is the fifth business day following the date of pricing of the Offered Bonds (such settlement being referred to as “T+5”). Pursuant to Rule 15c6-1 under the Exchange Act, trades in the secondary market generally are required to settle in two business days unless the parties to any such trade expressly agree otherwise. Accordingly, purchasers who wish to trade the Offered Bonds more than two business days prior to the scheduled settlement date will be required, by virtue of the fact that the Offered Bonds initially will settle in T+5, to specify an alternative settlement arrangement at the time of any such trade to prevent a failed settlement. Purchasers of the Offered Bonds who wish to trade the Offered Bonds prior to their date of delivery hereunder should consult their own advisors.

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LEGAL MATTERS

The legality of the shares offered hereby and certain other matters are passed upon for Avista by Marian M. Durkin, Esq., Senior Vice President, General Counsel, Corporate Secretary and Chief Compliance Officer of Avista, and Pillsbury Winthrop Shaw Pittman LLP, counsel to Avista. In giving its opinion, Pillsbury Winthrop Shaw Pittman LLP may rely as to matters governed by the Washington Business Corporation Act upon the opinion of Marian M. Durkin, Esq. Choate, Hall & Stewart LLP, Boston, Massachusetts, is acting as counsel to the underwriters.

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PROSPECTUS

AVISTA CORPORATION

Debt Securities

Preferred Stock

(no par value)

Common Stock

(no par value)

Avista Corporation may offer these securities from time to time on terms and at prices to be determined at the time of sale. The supplement to this prospectus relating to each offering will describe the specific terms of the securities being offered, as well as the terms of the offering and sale including the offering price.

Avista Corporation may sell these securities to or through underwriters, dealers or agents or directly to one or more purchasers.

Outstanding shares of Avista Corporation’s common stock are listed on the New York Stock Exchange under the symbol “AVA”. New shares of common stock will also be listed on the NYSE.

See “Risk Factors” on page 3 for reference to certain factors you should consider before investing in the securities.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus. Any representation to the contrary is a criminal offense.

The date of this Prospectus is February 25, 2016.

This prospectus incorporates by reference important business, financial and other information about Avista Corporation that is not included in or delivered with this prospectus. See “Where You Can Find More Information”. You may obtain copies of documents containing such information from us, without charge, by either calling or writing to us at:

Avista Corporation

Post Office Box 3727

Spokane, Washington 99220

Attention: Treasurer

Telephone: (509) 489-0500

TABLE OF CONTENTS

We have not authorized anyone to give you any information other than this prospectus, the accompanying prospectus supplement relating to an offering of specific securities and any written communication from us or any underwriters or agents specifying the final terms of such securities. You should assume that the information contained or incorporated by reference in this prospectus, the accompanying prospectus supplement and any such written communication is accurate only as of the respective dates of these documents. We are not offering to sell any securities and we are not soliciting offers to buy any securities in any jurisdiction in which offers are not permitted.

ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement that Avista Corporation filed with the Securities and Exchange Commission (the “SEC”), using the “shelf” registration process. Under this shelf registration process, we may, from time to time, sell the securities described in this prospectus in one or more offerings. This prospectus provides a general description of the securities we may offer. Each time we sell securities, we will provide a prospectus supplement that will contain specific information about the terms of that offering. That prospectus supplement may include or incorporate by reference a detailed and current discussion of any risk factors and will discuss any special considerations applicable to those securities, including the plan of distribution. The prospectus supplement may also add, update or change information contained in this prospectus. You should read both this prospectus and any prospectus supplement together with additional information described under “Where You Can Find More Information”. If there is any inconsistency between the information in this prospectus and any prospectus supplement or a document incorporated by reference herein filed after the date hereof or after the date of such prospectus supplement, you should rely on the information contained in that prospectus supplement or incorporated document, as the case may be.

References in the prospectus to the terms “we”, “us” or “Avista” or other similar terms mean Avista Corporation, unless we state otherwise or the context indicates otherwise.

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We may use this prospectus to offer from time to time:

The shares of Common Stock offered by this prospectus, together with the Debt Securities and the New Preferred Stock, are hereinafter sometimes called, collectively, “Securities”.

We may also offer hybrid securities that combine certain features of Securities of two or more classes.

Except in the case of hybrid Securities or as otherwise set forth in a supplement to this prospectus, the descriptions of the respective classes of Securities contained in this prospectus (and/or, in the case of the Common Stock, incorporated by reference herein) are independent, and no description of Securities of one class is relevant to an offering of Securities of another class.

For more detailed information about the Securities, you can read the exhibits to the registration statement. Those exhibits have been either filed with the registration statement or incorporated by reference to earlier SEC filings listed in the registration statement. See “Where You Can Find More Information”.

RISK FACTORS

Investing in the Securities involves risk. You should review all the information contained or incorporated by reference in this prospectus before deciding to invest. See “Where You Can Find More Information” herein. In particular, you should carefully consider the risks and uncertainties discussed in “Risk Factors”, “Forward-Looking Statements” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” in our annual and quarterly reports incorporated herein by reference.

In addition, you should carefully consider the risks and uncertainties discussed in the applicable prospectus supplement which relate to the specific Securities offered thereby.

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AVISTA CORPORATION

Avista Corporation, incorporated in the Territory of Washington in 1889, is primarily an electric and natural gas utility with certain other business ventures. Our corporate headquarters are in Spokane, Washington, the second-largest city in Washington. Spokane serves as the business, transportation, medical, industrial and cultural hub of the Inland Northwest region (eastern Washington and northern Idaho). Regional services include government and higher education, medical services, retail trade and finance. Through our subsidiary Alaska Electric Light and Power Company, we also provide electric utility services in the City and Borough of Juneau, Alaska.

We have two reportable business segments as follows:

We have other businesses, including a sheet metal fabrication business, emerging technology venture fund investments, commercial real estate investments and an inactive mining company. These activities do not represent a reportable business segment and are conducted by various direct and indirect subsidiaries of Avista Corporation most of which are subsidiaries of Avista Capital, Inc., which, in turn, is a direct wholly-owned subsidiary of Avista Corporation.

Reference is made to the documents incorporated herein by reference for detailed information regarding acquisitions and dispositions of subsidiaries, our investments in Avista Capital and other subsidiaries and the operating performance of each business segment (and other subsidiaries).

USE OF PROCEEDS

Unless we indicate differently in a supplement to this prospectus, Avista intends to use the net proceeds from the issuance and sale of the Securities offered by this prospectus for any or all of the following purposes: (a) to fund Avista Utilities’ construction, facility improvement and maintenance programs, (b) to refinance maturing long-term debt, (c) to continue to fund retirements (through redemption, purchase or acquisition) of long-term debt, (d) to repay short-term debt, (e) to accomplish other general corporate purposes permitted by law and (f) to reimburse Avista’s treasury for funds previously expended for any of these purposes.

DESCRIPTION OF THE BONDS

Avista may issue the Bonds in one or more series, or in one or more tranches within a series. The terms of the Bonds will include those stated in the Mortgage and those made part of the Mortgage by the Trust Indenture Act of 1939, as amended (the “Trust Indenture Act”). The following summary is not complete and is subject in all respects to the provisions of, and is qualified in its entirety by reference to, the Mortgage and the Trust

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Indenture Act. The Bonds, together with all other debt securities outstanding under the Mortgage, are hereinafter called, collectively, the “Mortgage Securities”. Avista has filed the Mortgage, as well as a form of supplemental indenture to the Mortgage to establish a series of Bonds, as exhibits to the registration statement of which this prospectus is a part. Capitalized terms used under this heading which are not otherwise defined in this prospectus have the meanings set forth in the Mortgage. Wherever particular provisions of the Mortgage or terms defined in the Mortgage are referred to, those provisions or definitions are incorporated by reference as part of the statements made in this prospectus and those statements are qualified in their entirety by that reference. Sections 125 through 150 of the Mortgage appear in the first supplemental indenture to the Original Mortgage. References to article and section numbers, unless otherwise indicated, are references to article and section numbers of the Mortgage.

The applicable prospectus supplement will describe the following terms of the Bonds of each series:

Payment and Paying Agents

Except as may be provided in the applicable prospectus supplement, Avista will pay interest, if any, on each Bond on each interest payment date to the person in whose name such Bond is registered (for purposes of this section of the prospectus, the registered holder of any Mortgage Security is herein referred to as a “Holder”) as of the close of business on the regular record date relating to such interest payment date; provided, however, that Avista will pay interest at maturity (whether at stated maturity, upon redemption or otherwise, “Maturity”) to the person to whom principal is paid.

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Unless otherwise specified in the applicable prospectus supplement, Avista will pay the principal of and premium, if any, and interest, if any, on the Bonds at Maturity upon presentation of the Bonds at the corporate trust office of Citibank, N.A. in New York, New York, as paying agent for Avista. Avista may change the place of payment of the Bonds, may appoint one or more additional paying agents (including Avista) and may remove any paying agent, all at its discretion.

Registration; Registration of Transfer

Unless otherwise specified in the applicable prospectus supplement, the Bonds will be issued only in fully registered form. The registered Holder will be treated as the owner of the Bond for all purposes under the Mortgage. Only registered Holders will have rights under the Mortgage. (Original Mortgage, Sec. 83)

The transfer of Bonds may be registered, and Bonds may be exchanged for other Bonds, upon surrender thereof at the principal office of Citibank, N.A. Avista may change any place for registration of transfer or exchange, and may designate an additional such place (including an office of Avista itself), in its discretion.

Except as otherwise provided in the applicable prospectus supplement, no service charge will be made for any registration of transfer or exchange of Bonds, but Avista may require payment of a sum sufficient to cover any tax or other governmental charge incident thereto. Avista will not be required to make any transfer or exchange of any Bonds for a period of 10 days next preceding any interest payment date or any selection of Bonds for redemption, nor will it be required to make transfers or exchanges of any Bonds which have been selected for redemption in whole or in part or as to which Avista shall have received a notice for the redemption thereof in whole or in part at the option of the Holder.

Redemption

The applicable prospectus supplement will indicate the extent, if any, to which the Bonds will be subject to (a) general redemption at the option of Avista or (b) special redemption by the application (either at the option of Avista or pursuant to the requirements of the Mortgage) of (x) cash deposited with the Mortgage Trustee as described under “Special Provisions for Retirement of Bonds” below or (y) cash deposited with the Mortgage Trustee in connection with the release of property from the lien of the Mortgage.

Notice of redemption will be given by mail not less than 30 days prior to the date fixed for redemption. (Original Mortgage, Sec. 52, as supplemented by the Fourteenth Supplemental Indenture)

If less than all the Bonds of a series are to be redeemed, the particular Bonds to be redeemed will be selected by the Mortgage Trustee by lot, according to such method as it shall deem proper in its discretion, or in such other manner as shall be specified with respect to any particular series. (Original Mortgage, Sec. 52; Forty-ninth Supplemental Indenture, Art. IV)

Any notice of redemption at the option of Avista may state that such redemption will be conditional upon receipt by the Mortgage Trustee, on or before the date fixed for such redemption, of money sufficient to pay the principal of and premium, if any, and interest, if any, on such Bonds and that if such money has not been so received, such notice will be of no force or effect and Avista will not be required to redeem such Bonds. (Original Mortgage, Sec. 52)

Issuance of Additional Mortgage Securities

In addition to the Bonds, other debt securities may be issued under the Mortgage. The present principal amount of debt securities which may be outstanding under the Mortgage is $10,000,000,000. However, Avista has reserved the right to amend the Mortgage (without any consent of or other action of Holders of any Mortgage Securities now or hereafter outstanding) to remove this limitation.

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Mortgage Securities of any series may be issued from time to time on the basis of:

Property additions generally include electric, natural gas, steam or water property acquired after May 31, 1939, but may not include property used principally for the production or gathering of natural gas. Any such property additions may be used if their ownership and operation is within the corporate purposes of Avista regardless of whether or not Avista has all the necessary permission it may need at any time from governmental authorities to operate such property additions.

The Mortgage provides that no reduction in the book value of the property recorded in the plant account of Avista shall constitute a property retirement, otherwise than in connection with physical retirements of property abandoned, destroyed or disposed of, and otherwise than in connection with the removal of such property in its entirety from the plant account.

No Mortgage Securities may be issued on the basis of property additions subject to prior liens, unless the prior lien bonds secured thereby have been qualified by being deducted from the Mortgage Securities otherwise issuable and do not exceed 66 2/3% of such property additions, and unless the Mortgage Securities then to be outstanding which have been issued against property subject to continuing prior liens and certain other items would not exceed 15% of the sum of the aggregate principal amount of all Mortgage Securities outstanding and all such prior lien bonds outstanding.

The amount of prior liens on mortgaged property acquired after the date of delivery of the Mortgage may be increased subsequent to the acquisition of such property provided that, if any property subject to such prior lien shall have been made the basis of any application under the Mortgage, all the additional obligations are deposited with the Mortgage Trustee or other holder of a prior lien.

(Original Mortgage, Secs. 4 through 8, 20 through 30, 46 and 120; First Supplemental Indenture, Sec. 2; Eleventh Supplemental Indenture, Sec. 5; Twelfth Supplemental Indenture, Sec. 1; Fourteenth Supplemental Indenture, Sec. 4; Seventeenth Supplemental Indenture, Sec. 3; Eighteenth Supplemental Indenture, Secs. 1, 2 and 6; Twenty-sixth Supplemental Indenture, Sec. 2; Twenty-ninth Supplemental Indenture, Art. II; Fifty-second Supplemental Indenture, Art. I)

Net Earnings Test

In general, Avista may not issue Mortgage Securities on the basis of property additions or cash unless net earnings for 12 consecutive months out of the preceding 18 calendar months (before income taxes, depreciation and amortization of property, property losses and interest on any indebtedness and amortization of debt discount and expense) are at least twice the annual interest requirements on all Mortgage Securities at the time outstanding, including the additional issue, and on all indebtedness of prior rank.

Avista is not required to satisfy the net earnings requirement prior to the issuance of Mortgage Securities on the basis of retired Mortgage Securities unless:

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In general, the Mortgage permits the inclusion of the following items in net earnings:

The Mortgage also provides that, in calculating net earnings, no deduction from revenues or other income shall be made for:

In general, the interest requirement on a new series of Mortgage Securities bearing interest at a variable interest rate or rates is determined by reference to the rate or rates to be in effect at the time of the initial issuance. However, if any outstanding Mortgage Securities or prior ranking indebtedness bears interest at a variable rate or rates, the annual interest requirements thereon are determined by reference to the rate or rates in effect on the date next preceding the date of issue of the new series of Mortgage Securities.

(Original Mortgage, Secs. 7, 28, 29 and 30; Twenty-ninth Supplemental Indenture, Sec. 3(b))

Security; Structural Subordination

The Bonds, together with all other Mortgage Securities now or hereafter issued under the Mortgage, will be secured by the Mortgage, which constitutes a first mortgage lien on Avista’s facilities for the generation, transmission and distribution of electric energy and the storage and distribution of natural gas and substantially all of Avista’s assets (except as stated below), subject to:

The assets excepted from the lien of the Mortgage include all cash and securities (including without limitation securities issued by Avista’s subsidiaries); merchandise, equipment, materials or supplies held for sale or consumption in Avista’s operations; receivables, contracts, leases and operating agreements; electric energy, and other material or products (including gas) generated, manufactured, produced or purchased by Avista, for sale, distribution or use in the ordinary course of its business. (Original Mortgage, Granting Clauses)

The Mortgage contains provisions for subjecting to the lien thereof all property (other than property of the kind excepted from such lien) acquired by Avista after the execution and delivery thereof, subject to purchase money liens and liens existing thereon at the time of acquisition and, subject to limitations in the case of consolidation, merger or sale of substantially all of Avista’s assets. (Original Mortgage, Granting Clauses and Art. XV)

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The Mortgage provides that the lien of the Mortgage shall not automatically attach to the properties of another corporation which shall have consolidated or merged with Avista in a transaction in which Avista shall be the surviving or resulting corporation. (Original Mortgage, Sec. 87)

The Mortgage provides that the Mortgage Trustee shall have a lien upon the mortgaged property, prior to the Mortgage Securities, for the payment of its reasonable compensation and expenses and for indemnity. (Original Mortgage, Secs. 92 and 97; First Supplemental Indenture, Art. XXV)

Although its utility operations are conducted directly by Avista, all of the other operations of Avista are conducted through its subsidiaries. The lien of the Mortgage does not cover the assets of the subsidiaries or the securities of the subsidiaries held by Avista. Any right of Avista, as a shareholder, to receive assets of any of its direct or indirect subsidiaries upon such subsidiary’s liquidation or reorganization (and the right of the Holders of the Bonds and other creditors of Avista to participate in those assets) is junior to the claims against such assets of that subsidiary’s creditors. As a result, the obligations of Avista to the holders of the Bonds and other creditors are effectively subordinated in right of payment to all indebtedness and other liabilities and commitments (including trade payables and lease obligations) of Avista’s direct and indirect subsidiaries.

Maintenance

The Mortgage provides that Avista will cause (or, with respect to property owned in common with others, make reasonable effort to cause) the mortgaged property to be maintained and kept in good repair, working order and condition, and will cause (or, with respect to property owned in common with others, make reasonable effort to cause) to be made such repairs, renewals and replacements of the mortgaged property as, in Avista’s judgment, may be necessary to operate the mortgaged property in accordance with common industry practice. Avista may discontinue, or cause or consent to the discontinuance of, the operation and maintenance of any of its properties if such discontinuance is, in the judgment of Avista, desirable in the conduct of its business. (Original Mortgage, Sec. 38)

Special Provisions for Retirement of Bonds

If, during any 12-month period, any of the mortgaged property is taken by eminent domain and/or sold to any governmental authority and/or sold pursuant to an order of a governmental authority, with the result that Avista receives $15,000,000 or more in cash or in principal amount of purchase money obligations, Avista is required to apply such cash and the proceeds of such obligations (subject to certain conditions and deductions, and to the extent not otherwise applied) to the redemption of Mortgage Securities which are, by their, terms, redeemable before maturity by the application of such cash and proceeds. (Original Mortgage, Sec. 64; Tenth Supplemental Indenture, Sec. 4)

Release and Substitution of Property

Unless Avista is in default in the payment of the interest on any Mortgage Securities then outstanding under the Mortgage, or a Completed Default (as defined below) shall have occurred and is continuing, Avista may obtain the release from the lien of the Mortgage of any mortgaged property upon the deposit of cash equal to the amount, if any, that the fair value of the property to be released exceeds the aggregate of:

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The use of obligations secured by purchase money mortgage as a credit in connection with the release of property, as described in clauses (1) and (4) above, is subject to the following limitations:

To the extent that property so released does not constitute funded property, the property additions used to effect the release will not, in certain cases, be deemed to constitute funded property, and the waiver of the right to issue Mortgage Securities to effect the release will, in certain cases, cease to be effective as such a waiver, all upon the satisfaction of certain conditions specified in the Mortgage. The Mortgage contains similar provisions as to cash proceeds of such property. The Mortgage also contains special provisions with respect to prior lien bonds pledged and disposition of moneys received on pledged bonds secured by a prior lien.

(Original Mortgage, Secs. 5; 31, 32, 46 through 50, 59, 60, 61, 118 and 134; Fifty-second Supplemental Indenture, Art. I)

Satisfaction and Discharge

Mortgage Securities will be deemed to have been paid for purposes of satisfaction of the lien of the Mortgage if there shall have been irrevocably deposited with the Mortgage Trustee for the payment or redemption of such Mortgage Securities:

to pay when due the principal of, premium, if any, and interest due and to become due on all outstanding Mortgage Securities on the maturity date or redemption date of such Mortgage Securities. For this purpose, “Government Obligations” include direct obligations of the government of the United States or obligations guaranteed by the government of the United States. (Original Mortgage, Sec. 106)

The Mortgage Trustee may, and upon request of Avista shall, cancel and discharge the lien of the Mortgage and reconvey the Mortgaged Property to Avista whenever all indebtedness secured thereby has been paid. (Original Mortgage, Sec. 106)

The right of Avista to cause its entire indebtedness in respect of the Mortgage Securities of any series to be deemed to be satisfied and discharged as described above will be subject to the satisfaction of conditions specified in the instrument creating such series.

Completed Defaults

Any of the following events will constitute a “Completed Default” under the Mortgage:

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The Mortgage Trustee may withhold notice of default (except in payment of principal, interest or funds for retirement of Mortgage Securities) if it determines that it is in the interest of the Holders. (Original Mortgage, Sec. 135)

Remedies

Acceleration of Maturity

If a Completed Default occurs and is continuing, the Mortgage Trustee may, and upon written request of the Holders of a majority in principal amount of Mortgage Securities then outstanding shall, declare the principal of, and accrued interest on, all outstanding Mortgage Securities immediately due and payable; provided, however, that the Holders of a majority in principal amount of outstanding Mortgage Securities may annul such declaration if before any sale of the mortgaged property:

Possession of Mortgaged Property

Under certain circumstances and to the extent permitted by law, if a Completed Default occurs and is continuing, the Mortgage Trustee has the power to take possession of, and to hold, operate and manage, the mortgaged property, or with or without entry, sell the mortgaged property. If the mortgaged property is sold, whether by the Mortgage Trustee or pursuant to judicial proceedings, the principal of the outstanding Mortgage Securities, if not previously due, will become immediately due. (Original Mortgage, Secs. 66, 67 and 71)

Right to Direct Proceedings

If a Completed Default occurs and is continuing, the Holders of a majority in principal amount of the Mortgage Securities then outstanding will have the right to direct the time, method and place of conducting any proceedings to be taken for any sale of the mortgaged property, the foreclosure of the Mortgage, or for the appointment of a receiver or any other proceeding under the Mortgage, provided that such direction does not conflict with any rule of law or with the Mortgage. (Original Mortgage, Sec. 69)

No Impairment of Right to Receive Payment

Notwithstanding any other provision of the Mortgage, the right of any Holder to receive payment of the principal of and interest on such Mortgage Security, or to institute suit for the enforcement of any such payment, shall not be impaired or affected without the consent of such Holder. (Original Mortgage, Sec. 148)

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Notice of Default

No Holder may enforce the lien of the Mortgage unless such Holder shall have given the Mortgage Trustee written notice of a Completed Default and unless the Holders of 25% in principal amount of the Mortgage Securities have requested the Mortgage Trustee in writing to act and have offered the Mortgage Trustee adequate security and indemnity and a reasonable opportunity to act. (Original Mortgage, Sec. 79)

Remedies Limited by State Law

The laws of the various states in which the property subject to the lien of the Mortgage is located may limit or deny the ability of the Mortgage Trustee and/or the Holders to enforce certain rights and remedies provided in the Mortgage in accordance with their terms.

Consolidation, Merger, Sale of Assets and Other Transactions

Avista may consolidate with or merge into any corporation having the corporate authority to carry on Avista’s business or convey, transfer or lease, subject to the lien of the Mortgage, all or substantially all of the mortgaged property as an entirety to any corporation lawfully entitled to acquire or lease or operate the same; provided, however, that (1) such transaction shall not impair the lien of the Mortgage or the rights of the Mortgage Trustee or the Holders under the Mortgage; (2) any such lease shall be subject to termination by the Mortgage Trustee during the continuance of a Completed Default; and (3) upon any such consolidation, merger or transfer, or any such lease that extends beyond the maturity of the Mortgage Securities then outstanding, the surviving corporation, transferee or lessee shall assume the covenants of Avista to pay the principal of and interest on the Mortgage Securities and perform all other covenants of Avista under the Mortgage. (Original Mortgage, Sec. 85)

Upon any consolidation, merger, conveyance or transfer described in the preceding paragraph, the Mortgage will not become a lien on any properties of the successor or transferee corporation except (1) those acquired by it from Avista and improvements, extensions and additions thereto and renewals and replacements thereof, (2) property made and used by it as the basis for the authentication and delivery of Mortgage Securities, the withdrawal of cash or the release of property and (3) property acquired or constructed by it to maintain, review or preserve the mortgaged property. (Original Mortgage, Sec. 87)

Nothing in the Mortgage prevents any consolidation or merger after which Avista would be the surviving or resulting corporation or any conveyance, transfer or lease of any part of the mortgaged property which does not constitute the entirety, or substantially the entirety, thereof. (Twenty-ninth Supplemental Indenture, Art. II, Sec. 3(e)(i))

If Avista shall enter into a transaction contemplated in the preceding paragraph, unless Avista, in its discretion, enters into a supplemental indenture that provides otherwise, the Mortgage will not become a lien on any of the properties acquired by Avista in or as a result of such transaction or any improvements, extensions or additions thereto or any renewals or replacements thereof. (Twenty-ninth Supplemental Indenture, Art. II, Sec. 3(e)(ii))

Modification

Modifications Without Consent

Avista and the Mortgage Trustee may enter into one or more supplemental indentures without the consent of any Holders for any of the following purposes:

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(Original Mortgage, Sec. 120; Twenty-sixth Supplemental Indenture, Sec. 2; Twenty-ninth Supplemental Indenture, Article II)

Modification With Consent

In general, the Mortgage, the rights and obligations of Avista and the rights of the Holders may be modified with the consent of 60% in principal amount of the Mortgage Securities outstanding, and, if less than all series of Mortgage Securities are affected, the consent also of 60% in principal amount of the Mortgage Securities of each series affected. However, no modification of the terms of payment of principal or interest, and no modification affecting the lien or reducing the percentage required for modification, is effective against any Holder without its consent. (Original Mortgage, Art. XVIII, Sec. 149; First Supplemental Indenture, Sec. 10)

Concerning the Mortgage Trustee

The Mortgage Trustee has, and is subject to, all the duties and responsibilities specified with respect to an indenture trustee under the Trust Indenture Act. Subject to such provisions, the Mortgage Trustee is not under any obligation to take any action in respect of any default or otherwise, or toward the execution or enforcement of any of the trusts created by the Mortgage, or to institute, appear in or defend any suit or other proceeding in connection therewith, unless requested in writing so to do by the Holders of a majority in principal amount of the Mortgage Securities then outstanding. Anything in the Mortgage to the contrary notwithstanding, the Mortgage Trustee is under no obligation or duty to perform any act thereunder (other than the delivery of certain notices) or to institute or defend any suit in respect hereof, unless properly indemnified to its satisfaction. (Original Mortgage, Sec. 92)

The Mortgage Trustee may at any time resign and be discharged of the trusts created by the Mortgage by giving written notice to Avista and thereafter publishing notice thereof, specifying a date when such resignation shall take effect, as provided in the Mortgage, and such resignation shall take effect upon the day specified in such notice unless a successor trustee shall have previously been appointed by the Holders or Avista and in such event such resignation shall take effect immediately upon the appointment of such successor trustee. The Mortgage Trustee may be removed at any time by the Holders of a majority in principal amount of the Mortgage Securities then outstanding. (Original Mortgage, Secs. 100 and 101)

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If Avista appoints a successor trustee and such successor trustee has accepted the appointment, the Mortgage Trustee will be deemed to have resigned as of the date of such successor trustee’s acceptance. (Original Mortgage, Sec. 102)

Evidence of Compliance with Mortgage Provisions

Compliance with provisions of the Mortgage is evidenced by written statements of Avista’s officers or persons selected or paid by Avista. In certain matters, statements must be made by an independent accountant or engineer. Various certificates and other papers are required to be filed annually and upon the happening of certain events, including an annual certificate with reference to compliance with the terms of the Mortgage and absence of Completed Defaults.

DESCRIPTION OF THE NOTES

Avista may issue the Notes in one or more series, or in one or more tranches within a series. The terms of the Notes will include those stated in the Indenture and those made part of the Indenture by the Trust Indenture Act. The following summary is not complete and is subject in all respects to the provisions of, and is qualified in its entirety by reference to, the Indenture and the Trust Indenture Act. The Notes, together with all other debt securities outstanding under the Indenture, are hereinafter called, collectively, the “Indenture Securities”. Avista has filed the Indenture, as well as a form of officer’s certificate to establish a series of Notes, as exhibits to the registration statement of which this prospectus is a part. Capitalized terms used under this heading which are not otherwise defined in this prospectus have the meanings set forth in the Indenture. Wherever particular provisions of the Indenture or terms defined in the Indenture are referred to, those provisions or definitions are incorporated by reference as part of the statements made in this prospectus and those statements are qualified in their entirety by that reference. References to article and section numbers, unless otherwise indicated, are references to article and section numbers of the Indenture.

The applicable prospectus supplement or prospectus supplements will describe the following terms of the Notes of each series or tranche:

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Payment and Paying Agents

Except as may be provided in the applicable prospectus supplement, Avista will pay interest, if any, on each Note on each interest payment date to the person in whose name such Note is registered (for the purposes of this section of the prospectus, the registered holder of any Indenture Security is herein referred to as a “Holder”) as of the close of business on the regular record date relating to such interest payment date; provided, however, that Avista will pay interest at maturity (whether at stated maturity, upon redemption or otherwise, “Maturity”) to the person to whom principal is paid. However, if there has been a default in the payment of interest on any Note, such defaulted interest may be payable to the Holder of such Note as of the close of business on a date selected by the Indenture Trustee which is not more than 30 days and not less than 10 days before the date proposed by Avista for payment of such defaulted interest or in any other lawful manner not inconsistent with the requirements of any securities exchange on which such Note may be listed, if the Indenture Trustee deems such manner of payment practicable. (Indenture, Sec. 307)

Unless otherwise specified in the applicable prospectus supplement, Avista will pay the principal of and premium, if any, and interest, if any, on the Notes at Maturity upon presentation of the Notes at the corporate trust office of The Bank of New York in New York, New York, as paying agent for Avista. Avista may change the place of payment of the Notes, may appoint one or more additional paying agents (including Avista) and may remove any paying agent, all at its discretion. (Indenture, Sec. 502)

Registration; Registration of Transfer

The Notes will be issued only in fully registered form. The registered Holder of a Note will be treated as the owner of the Note for all purposes under the Indenture. Only registered Holders will have rights under the Indenture. (Indenture, Sec. 308)

Unless otherwise specified in the applicable prospectus supplement, Holders may register the transfer of Notes, and may exchange Notes for other Notes of the same series and tranche, of authorized denominations and having the same terms and aggregate principal amount, at the corporate trust office of The Bank of New York in New York, New York, as security registrar for the Notes. Avista may change the place for registration of transfer and exchange of the Notes, may appoint one or more additional security registrars (including Avista) and may remove any security registrar, all at its discretion. (Indenture, Sec. 305 and 502)

Except as otherwise provided in the applicable prospectus supplement, no service charge will be made for any transfer or exchange of the Notes, but Avista may require payment of a sum sufficient to cover any tax or other governmental charge that may be imposed in connection with any registration of transfer or exchange of the Notes. Avista will not be required to execute or to provide for the registration of transfer or the exchange of (a) any Note during a period of 15 days before giving any notice of redemption or (b) any Note selected for redemption in whole or in part, except the unredeemed portion of any Note being redeemed in part. (Indenture, Sec. 305)

Redemption

The applicable prospectus supplement will set forth any terms for the optional or mandatory redemption of Notes. Except as otherwise provided in the applicable prospectus supplement with respect to Notes redeemable at

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the option of the Holder, Notes will be redeemable by Avista only upon notice by mail not less than 30 nor more than 60 days before the date fixed for redemption. If less than all the Notes of a series, or any tranche thereof, are to be redeemed by Avista, the particular Notes to be redeemed will be selected by such method as shall be provided for such series or tranche, or in the absence of any such provision, by such method of random selection as the Security Registrar deems fair and appropriate. (Indenture, Secs. 403 and 404)

Any notice of redemption at the option of Avista may state that such redemption will be conditional upon receipt by the paying agent or agents, on or before the date fixed for such redemption, of money sufficient to pay the principal of and premium, if any, and interest, if any, on such Notes and that if such money has not been so received, such notice will be of no force or effect and Avista will not be required to redeem such Notes. (Indenture, Sec. 404)

Unsecured Obligations; Structural Subordination

The Indenture is not a mortgage or other lien on assets of Avista or its subsidiaries. In addition to the Notes, other debt securities may be issued under the Indenture, without any limit on the aggregate principal amount. Each series of Indenture Securities will be unsecured and will rank pari passu with all other series of Indenture Securities, except as otherwise provided in the Indenture, and with all other unsecured and unsubordinated indebtedness of Avista. Except as otherwise described in the applicable prospectus supplement, the Indenture does not limit the incurrence or issuance by Avista of other secured or unsecured debt, whether under the Indenture, under any other indenture that Avista may enter into in the future or otherwise.

Although its utility operations are conducted directly by Avista, all of the other operations of Avista are conducted through its subsidiaries. Any right of Avista, as a shareholder, to receive assets of any of its direct or indirect subsidiaries upon the subsidiary’s liquidation or reorganization (and the right of the Holders and other creditors of Avista to participate in those assets) is junior to the claims against such assets of that subsidiary’s creditors. As a result, the obligations of Avista to the Holders and other creditors are effectively subordinated in right of payment to all indebtedness and other liabilities and commitments (including trade payables and lease obligations) of Avista’s direct and indirect subsidiaries.

Satisfaction and Discharge

Any Indenture Securities, or any portion of the principal amount thereof, will be deemed to have been paid for purposes of the Indenture and, at Avista’s election, the entire indebtedness of Avista in respect thereof will be deemed to have been satisfied and discharged, if there shall have been irrevocably deposited in trust with the Indenture Trustee or any paying agent (other than Avista):

to pay when due the principal of and premium, if any, and interest, if any, due and to become due on such Indenture Securities. For this purpose, “Eligible Obligations” include direct obligations of, or obligations unconditionally guaranteed by, the United States, entitled to the benefit of the full faith and credit thereof and certificates, depositary receipts or other instruments which evidence a direct ownership interest in such obligations or in any specific interest or principal payments due in respect thereof and such other obligations or instruments as shall be specified in an accompanying prospectus supplement. (Indenture, Sec. 601)

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The right of Avista to cause its entire indebtedness in respect of the Indenture Securities of any series to be deemed to be satisfied and discharged as described above will be subject to the satisfaction of conditions specified in the instrument creating such series.

The Indenture will be deemed to have been satisfied and discharged when no Indenture Securities remain outstanding thereunder and Avista has paid or caused to be paid all other sums payable by Avista under the Indenture. (Indenture, Sec. 602)

Events of Default

Any one or more of the following events with respect to a series of Indenture Securities that has occurred and is continuing will constitute an “Event of Default” with respect to such series of Indenture Securities:

Remedies

Acceleration of Maturity

If an Event of Default applicable to the Indenture Securities of any series occurs and is continuing, then either the Indenture Trustee or the Holders of not less than 33% in aggregate principal amount of the outstanding Indenture Securities of such series may declare the principal amount (or, if any of the outstanding Indenture Securities of such series are Discount Securities, such portion of the principal amount thereof as may be specified

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in the terms thereof) of all of the outstanding Indenture Securities of such series to be due and payable immediately by written notice to Avista (and to the Indenture Trustee if given by the Holders); provided, however, that if an Event of Default occurs and is continuing with respect to more than one series of Indenture Securities, the Indenture Trustee or the Holders of not less than 33% in aggregate principal amount of the outstanding Indenture Securities of all such series, considered as one class, may make such declaration of acceleration and not the Holders of any one such series.

At any time after such a declaration of acceleration with respect to the Indenture Securities of any series has been made, but before a judgment or decree for payment of the money due has been obtained, such declaration and its consequences will, without further act, be deemed to have been rescinded and annulled, if:

Right to Direct Proceedings

If an Event of Default with respect to the Indenture Securities of any series occurs and is continuing, the Holders of a majority in principal amount of the outstanding Indenture Securities of such series will have the right to direct the time, method and place of conducting any proceedings for any remedy available to the Indenture Trustee in exercising any trust or power conferred on the Indenture Trustee; provided, however, that if an Event of Default occurs and is continuing with respect to more than one series of Indenture Securities, the Holders of a majority in aggregate principal amount of the outstanding Indenture Securities of all such series, considered as one class, will have the right to make such direction, and not the Holders of any one of such series; and provided, further, that (a) such direction does not conflict with any rule of law or with the Indenture, and could not involve the Indenture Trustee in personal liability in circumstances where indemnity would not, in the Indenture Trustee’s sole discretion, be adequate and (b) the Indenture Trustee may take any other action deemed proper by the Indenture Trustee which is not inconsistent with such direction. (Indenture, Sec. 712)

Limitation on Right to Institute Proceedings

No Holder will have any right to institute any proceeding, judicial or otherwise, with respect to the Indenture or for the appointment of a receiver or for any other remedy thereunder unless:

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Furthermore, no Holder of any series of Indenture Securities will be entitled to institute any such action if and to the extent that such action would disturb or prejudice the rights of other Holders of such series. (Indenture, Sec. 707)

No Impairment of Right to Receive Payment

Notwithstanding that the right of a Holder to institute a proceeding with respect to the Indenture is subject to certain conditions precedent, each Holder will have the right, which is absolute and unconditional, to receive payment of the principal of and premium, if any, and interest, if any, on such Indenture Security when due and to institute suit for the enforcement of any such payment. Such rights may not be impaired or affected without the consent of such Holder. (Indenture, Sec. 708)

Notice of Default

The Indenture Trustee is required to give the Holders notice of any default under the Indenture to the extent required by the Trust Indenture Act, unless such default shall have been cured or waived, except that no such notice to Holders of a default of the character described in the third bulleted paragraph under “— Events of Default” may be given until at least 75 days after the occurrence thereof. For purposes of the preceding sentence, the term “default” means any event which is, or after notice or lapse of time, or both, would become, an Event of Default. The Trust Indenture Act currently permits the Indenture Trustee to withhold notices of default (except for certain payment defaults) if the Indenture Trustee in good faith determines the withholding of such notice to be in the interests of the Holders. (Indenture, Sec. 802)

Consolidation, Merger, Sale of Assets and Other Transactions

Avista may not consolidate with or merge into any other Person, or convey or otherwise transfer, or lease, all of its properties, as or substantially as an entirety, to any Person, unless:

In the case of the conveyance or other transfer of all of the properties of Avista, as or substantially as an entirety, to any person as contemplated above, Avista would be released and discharged from all obligations under the Indenture and on all Indenture Securities then outstanding unless Avista elects to waive such release and discharge. Upon any such consolidation or merger or any such conveyance or other transfer of properties of Avista, the successor, transferee or lessee would succeed to, and be substituted for, and would be entitled to exercise every power and right of, Avista under the Indenture. (Indenture, Secs. 1001, 1002 and 1003)

For purposes of the Indenture, the conveyance, transfer or lease by Avista of all of its facilities (a) for the generation of electric energy, (b) for the transmission of electric energy, (c) for the distribution of electric energy and/or natural gas, in each case considered alone, (d) all of its facilities described in clauses (a) and (b),

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considered together, or (e) all of its facilities described in clauses (b) and (c), considered together, will in no event be deemed to constitute a conveyance or other transfer of all the properties of Avista, as or substantially as an entirety, unless, immediately following such conveyance, transfer or lease, Avista owns no unleased properties in the other such categories of property not so conveyed or otherwise transferred or leased. (Indenture, Sec. 1001)

The Indenture will not prevent or restrict:

If Avista conveys or otherwise transfers any part of its properties which does not constitute the entirety, or substantially the entirety, thereof to another Person meeting the requirements set forth in the first paragraph under this heading, and if:

then Avista would be released and discharged from all obligations and covenants under the Indenture and on all Indenture Securities then outstanding unless Avista elects to waive such release and discharge. In such event, the transferee would succeed to, and be substituted for, and would be entitled to exercise every right and power of, Avista under the Indenture. (Indenture, Sec. 1005)

Modification of Indenture

Modifications Without Consent

Avista and the Indenture Trustee may enter into one or more supplemental indentures, without the consent of any Holders, for any of the following purposes:

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Without limiting the generality of the foregoing, if the Trust Indenture Act is amended after the date of the Original Indenture in such a way as to require changes to the Indenture or the incorporation therein of additional provisions or so as to permit changes to, or the elimination of, provisions which, at the date of the Original Indenture or at any time thereafter, were required by the Trust Indenture Act to be contained in the Indenture, the Indenture will be deemed to have been amended so as to conform to such amendment or to effect such changes or elimination, and Avista and the Indenture Trustee may, without the consent of any Holders, enter into one or more supplemental indentures to evidence or effect such amendment. (Indenture, Sec. 1101)

Modifications Requiring Consent

Except as provided above, the consent of the Holders of a majority in aggregate principal amount of the Indenture Securities of all series then outstanding, considered as one class is required for the purpose of adding any provisions to, or changing in any manner, or eliminating any of the provisions of, the Indenture pursuant to one or more supplemental indentures; provided, however, that if less than all of the series of Indenture Securities outstanding are directly affected by a proposed supplemental indenture, then the consent only of the Holders of a majority in aggregate principal amount of outstanding Indenture Securities of all series so directly affected, considered as one class, will be required; and provided, further, that if the Indenture Securities of any series have been issued in more than one tranche and if the proposed supplemental indenture directly affects the rights of the Holders of one or more, but less than all, of such tranches, then the consent only of the Holders of a majority in aggregate principal amount of the outstanding Indenture Securities of all tranches so directly affected, considered as one class, will be required; and provided, further, that no such amendment or modification may:

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A supplemental indenture which changes or eliminates any covenant or other provision of the Indenture which has expressly been included solely for the benefit of the Holders of, or which is to remain in effect only so long as there shall be outstanding, Indenture Securities of one or more specified series, or one or more tranches thereof, or modifies the rights of the Holders of such series or tranche with respect to such covenant or other provision, will be deemed not to affect the rights under the Indenture of the Holders of any other series or tranche.

If the supplemental indenture or other document establishing any series or tranche of Indenture Securities so provides, and as specified in the applicable prospectus supplement and/or pricing supplement, the Holders of such Indenture Securities will be deemed to have consented, by virtue of their purchase of such Indenture Securities, to a supplemental indenture containing the additions, changes or eliminations to or from the Indenture which are specified in such supplemental indenture or other document. No Act of such Holders will be required to evidence such consent and such consent may be counted in the determination of whether the Holders of the requested principal amount of Indenture Securities have consented to such supplemental indenture. (Indenture, Sec. 1102)

Duties of the Indenture Trustee; Resignation; Removal

The Indenture Trustee has, and is subject to, all the duties and responsibilities specified with respect to an indenture trustee under the Trust Indenture Act. Subject to such provisions, the Indenture Trustee will be under no obligation to exercise any of the powers vested in it by the Indenture at the request of any Holder, unless such Holder offers it reasonable indemnity against the costs, expenses and liabilities which might be incurred thereby. The Indenture Trustee will not be required to expend or risk its own funds or otherwise incur personal financial liability in the performance of its duties if the Indenture Trustee reasonably believes that repayment or adequate indemnity is not reasonably assured to it. (Indenture, Secs. 801 and 803)

The Indenture Trustee may resign at any time with respect to the Indenture Securities of one or more series by giving written notice thereof to Avista or may be removed at any time with respect to the Indenture Securities of one or more series by Act of the Holders of a majority in principal amount of the outstanding Indenture Securities of such series delivered to the Indenture Trustee and Avista. No resignation or removal of the Indenture Trustee and no appointment of a successor trustee will become effective until the acceptance of appointment by a successor trustee in accordance with the requirements of the Indenture. So long as no Event of Default or event which, after notice or lapse of time, or both, would become an Event of Default has occurred and is continuing, if Avista has delivered to the Indenture Trustee with respect to one or more series a resolution of its Board of Directors appointing a successor trustee with respect to that or those series and such successor has

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accepted such appointment in accordance with the terms of the Indenture, the Indenture Trustee with respect to that or those series will be deemed to have resigned and the successor will be deemed to have been appointed as trustee in accordance with the Indenture. (Indenture, Sec. 810)

Evidence of Compliance

Compliance with the Indenture provisions is evidenced by written statements of Avista officers or persons selected or paid by Avista. In certain cases, Avista must furnish opinions of counsel and certifications of an engineer, appraiser or other expert (who in some cases must be independent). In addition, the Indenture requires that Avista give the Indenture Trustee, not less than annually, a brief statement as to Avista’s compliance with the conditions and covenants under the Indenture.

Governing Law

The Indenture and the Indenture Securities are governed by and construed in accordance with the laws of the State of New York, except to the extent that the Trust Indenture Act is applicable.

Relationship with the Indenture Trustee

In addition to acting as Indenture Trustee, The Bank of New York Mellon has various banking and trust relationships with Avista.

DESCRIPTION OF PREFERRED STOCK

General

The authorized capital stock of Avista Corporation, as set forth in the Articles, consists of 10,000,000 shares of Preferred Stock, cumulative, without nominal or par value, which is issuable in series, and 200,000,000 shares of Common Stock, without nominal or par value. Following is a brief description of certain of the rights and privileges of the Preferred Stock.

Avista may issue shares of New Preferred Stock in one or more additional series. The terms of the New Preferred Stock will include those stated in the Articles and the Bylaws and those made applicable thereto by the Washington BCA. The following summary is not complete and is subject in all respects to the provisions of, and is qualified in its entirety by reference to, the Articles, the Bylaws and the Washington BCA. Avista has filed the Articles and the Bylaws as exhibits to the registration statement of which this prospectus is a part. Whenever particular provisions of the Articles or the Bylaws are referred to, those provisions are incorporated by reference as part of the statements made in this prospectus and those statements are qualified in their entirety by that reference.

The Articles provide that the Preferred Stock may be divided into and issued from time to time in one or more series. All shares of Preferred Stock constitute one and the same class of stock, are of equal rank and will otherwise be identical except as to the designation thereof, the date or dates from which dividends on shares thereof will be cumulative, and except that each series may vary as to, and the applicable prospectus supplement will describe:

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When Preferred Stock of a new series is to be issued, the number of shares constituting such series, its distinguishing serial designation and its particular characteristics (insofar as there may be variations between series) may be fixed by resolution of the Board of Directors.

Dividend Rights

The New Preferred Stock of each series will be entitled, on a parity with each other series of Preferred Stock and in preference to the Common Stock, to receive, but only when and as declared by the Board of Directors, dividends at the rate determined for such series and set forth in the applicable prospectus supplement. Such dividends will be cumulative from the date of issuance of the New Preferred Stock and will be payable on the fifteenth day of March, June, September and December in each year, except as otherwise provided in the applicable prospectus supplement.

Liquidation Rights

The New Preferred Stock of each series will be entitled, upon dissolution or liquidation, on a parity with each other series of Preferred Stock and in preference to the Common Stock, to a liquidation preference per share determined for such series plus an amount equivalent to accrued and unpaid dividends thereon, if any, to the date of such event. The liquidation preference of each series of New Preferred Stock will be set forth in the applicable prospectus supplement.

Voting Rights

Except for those purposes for which the right to vote is expressly conferred by the Articles or the Washington BCA, the holders of Preferred Stock have no power to vote.

Under the Articles, whenever and as often as, at any date, dividends payable on any shares of Preferred Stock (including any New Preferred Stock) shall be in arrears in an amount equal to the aggregate amount of dividends accumulated on such shares over the eighteen (18) month period ended on such date, the holders of the Preferred Stock of all series, voting separately and as a single class, are entitled to elect a majority of the Board of Directors, and the holders of the Common Stock, voting separately and as a single class, shall be entitled to elect the remaining directors. Such voting rights of the holders of the Preferred Stock cease when all defaults in the payment of dividends on the Preferred Stock of any and all series have been cured. See “Description of Common Stock — Voting Rights – Election of Directors” for additional information with respect to the election of directors.

In addition, under the Articles the affirmative vote of the holders of at least a majority of the shares of the Preferred Stock is required:

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Under the Washington BCA, the approval of the holders of a majority of the outstanding shares of Preferred Stock is required in connection with certain changes in the capital structure of Avista or in certain rights and preferences of the Preferred Stock, including certain of the changes described in (a) above. In addition, the Washington BCA requires the approval of certain mergers, share exchanges and other major corporate transactions by the holders of two-thirds of the outstanding Preferred Stock.

Pre-emptive Rights

No holder of Preferred Stock has any pre-emptive rights.

Miscellaneous

The Articles contain no restriction on the redemption or repurchase by Avista of shares of Preferred Stock while there is any arrearage in the payment of dividends on, or sinking fund payments in respect of, the Preferred Stock.

Upon issuance as contemplated by this prospectus and the applicable prospectus supplement, the New Preferred Stock will be fully paid and nonassessable. The holders of the New Preferred Stock will not be subject to liability for further calls or assessment by, or for liabilities of, Avista.

DESCRIPTION OF COMMON STOCK

General

The authorized capital stock of Avista, as set forth in the Articles, consists of 10,000,000 shares of Preferred Stock, cumulative, without nominal or par value, which is issuable in series, and 200,000,000 shares of Common Stock without nominal or par value. Following is a brief description of certain of the rights and privileges of the Common Stock.

Avista may issue additional shares of its Common Stock from time to time. The terms of the Common Stock include those stated in the Articles and the Bylaws and those made applicable thereto by the Washington BCA. The following summary is not complete and is subject in all respects to the provisions of, and is qualified in its entirety by reference to, the Articles, the Bylaws and the Washington BCA. Avista has filed the Articles and the Bylaws as exhibits to the registration statement of which this prospectus forms a part. Whenever particular provisions of the Articles or the Bylaws are referred to, those provisions are incorporated as part of the statements made in this prospectus and those statements are qualified in their entirety by that reference.

The description of the Common Stock set forth below in this prospectus is also set forth in Post-Effective Amendment No. 1 on Form 10/A, filed by Avista with the SEC on February 25, 2015, to Avista’s registration

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statement on Form 10, filed by Avista with the SEC in September 1952. That description is incorporated in this prospectus by reference. If Avista amends the Articles or Bylaws, or if the Washington BCA is amended, after the date of this prospectus in a way that would make such description of the Common Stock inaccurate in any material respect, Avista will further amend such registration statement on Form 10 to update the description of the Common Stock, and such further amendment will be incorporated in this prospectus by reference.

Dividend Rights; Rights upon Liquidation; No Pre-Emptive Rights

After full provision for all Preferred Stock dividends declared or in arrears, the holders of Common Stock are entitled to receive such dividends as may be lawfully declared from time to time by the Board of Directors.

In the event of any liquidation or dissolution of Avista, after satisfaction of the preferential liquidation rights of the Preferred Stock (including accumulated dividends), the holders of Common Stock would be entitled to share ratably in all assets of Avista available for distribution to shareholders.

No holder of Common Stock has any pre-emptive rights.

Voting Rights

General; Quorum

The holders of the Common Stock have sole voting power, except as indicated below or as otherwise provided by law. Each holder of Common Stock is entitled to one vote per share.

Election of Directors

In an uncontested election of directors, each vote may be cast “for” or “against” one or more candidates, or a shareholder may “abstain” with respect to one or more candidates. A candidate is elected to the Board of Directors only if the number of votes “for” such candidate exceeds the number of votes “against” such candidate. Shares otherwise present at the meeting but for which there is an “abstention” or as to which no authority or direction is given or specified with respect to a candidate are not counted as votes “for” or “against”. If an incumbent director does not receive a majority of votes cast, he or she would continue to serve a term that would terminate on the date that is the earliest of (a) the date of the commencement of the term of a new director selected by the Board to fill the office held by such director, (b) the effective date of the resignation of such director and (c) the later of (i) the last day of the sixth calendar month commencing after the election and (ii) December 31 of the calendar year in which the election occurred. In a contested election — that is, an election in which the number of candidates exceeds the total number of directors to be elected — shareholders would be allowed to vote “for” one or more candidates (not to exceed the number of directors to be elected) or “withhold” votes with respect to one or more candidates. The candidates elected would be those receiving the largest number of votes (up to the number of directors to be elected). Shareholders are not allowed to cumulate their votes in any election of directors (whether or not contested).

Senior Class of Stock; Major Corporate Transaction

Under the Articles, the approval of the holders of the majority of the outstanding shares of Common Stock is required to create a new class of stock, including, for example, preference stock or any other class of stock senior to the Common Stock. In addition, in any circumstance in which the Washington BCA would require the approval of shareholders to authorize (1) the merger of Avista with or into another entity or a statutory share exchange with another entity, (2) a sale, lease, exchange or other disposition of property of Avista or (3) the dissolution of Avista, the requisite shareholder approval (in addition to any required approval by the holders of Preferred Stock) is the affirmative vote of the holders of a majority of the outstanding shares of Common Stock, unless the Washington BCA requires a higher standard.

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Voting Rights of Preferred Stock

Under the Articles, whenever and as often as, at any date, dividends payable on any shares of Preferred Stock (including any New Preferred Stock) shall be in arrears in an amount equal to the aggregate amount of dividends accumulated on such shares of Preferred Stock over the eighteen (18) month period ended on such date, the holders of the Preferred Stock, voting separately and as a single class, are entitled to elect a majority of the Board of Directors, and the holders of the Common Stock, voting separately and as a single class, are entitled to elect the remaining directors. Such voting rights of the holders of the Preferred Stock cease when all defaults in the payment of dividends on the Preferred Stock have been cured.

In addition, the consent of various proportions of the Preferred Stock at the time outstanding is required to adopt any amendment to the Articles which would authorize any new class of stock ranking prior to or on a parity with the Preferred Stock as to certain matters, to increase the authorized number of shares of the Preferred Stock, to change any of the rights or preferences of outstanding Preferred Stock or to issue additional shares of Preferred Stock unless an earnings test is satisfied.

Under the Washington BCA, the approval of the holders of a majority of the outstanding shares of Preferred Stock is required in connection with certain changes in the capital structure of Avista or in certain rights and preferences of the Preferred Stock, including certain of the changes referred to in the preceding paragraph. In addition, the Washington BCA requires approval of certain mergers, share exchanges and other major corporate transactions by the holders of two-thirds of the outstanding Preferred Stock.

Board of Directors

The Articles provide that the number of directors of the Company will be the number, not to exceed eleven, as the Board of Directors specifies from time to time in the Bylaws, subject to the rights of holders of the Preferred Stock to elect directors in certain circumstances. Both the Articles and the Bylaws provide that all directors will be elected at each annual meeting for a term that will expire at the next succeeding annual meeting.

Vacancies occurring in the Board of Directors may be filled by the Board. Directors may be removed only for cause and only if the number of votes cast by holders of Common Stock for the removal of a director exceeds the number of votes cast against such removal.

The Articles and the Bylaws further require an affirmative vote of the holders of at least 80% of the outstanding shares of Common Stock to alter, amend or repeal the provisions relating to the Board of Directors and the filling of vacancies on, and the removal of members from, the Board of Directors.

Advance Notice of Shareholder Nominations for Director and Proposals of Other Business

Under the Bylaws, at an annual meeting of shareholders only such nominations of individuals for election to the Board of Directors shall be made as shall have been properly made and only such other business shall be transacted as shall be properly brought before the meeting, in accordance with the timing and information requirements set forth in the Bylaws. In general, a shareholder’s notice of intention to nominate a candidate for director or bring other business before the meeting must be delivered in writing not less than 90 nor more than 180 days prior to the first anniversary date of the preceding year’s annual meeting, and the information contained in or accompanying such notice shall be updated periodically up to the time of the meeting. Only shareholders of record (as of the date of the notice and the date of the meeting) who have complied with the procedures set forth in the Bylaws and appear at the meeting in person or by qualified representative are eligible to nominate a candidate for director or bring other business before the meeting.

A shareholder notice must contain information regarding the proponent, the nominee (if any) and their respective shareholdings and derivative transactions and, in addition, information as to:

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A shareholder proposing to nominate an individual for election as a director must submit a questionnaire (similar to Avista’s directors’ and officers’ questionnaire) completed and signed by the nominee, which also includes representations by the nominee concerning (i) the absence of certain voting commitments and compensation or indemnification arrangements and (ii) the nominee’s compliance with the applicable law and Avista’s policies.

Proposed business will not be transacted and proposed nominations will not be made if the shareholder (or qualified representative) does not appear at the meeting and satisfy the other requirements of the Bylaws.

These procedures and information requirements apply to any nomination to be made at, or other business to be brought before, a shareholder meeting, including any proposal that is to be included in Avista’s Proxy Statement pursuant to Rule 14a-8 under the Exchange Act.

Special Meetings of Shareholders

The Articles provide that a special meeting of shareholders may be called by certain corporate officers and shall be called by the President at the request of the holders of two-thirds of the outstanding shares of Common Stock.

“Fair Price” Provision

The Articles contain a “fair price” provision which requires the affirmative vote of the holders of at least 80% of the outstanding shares of Common Stock for the consummation of certain business combinations, including mergers, consolidations, recapitalizations, certain dispositions of assets, certain issuances of securities, liquidations and dissolutions involving Avista and a person or entity who is or, under certain circumstances, was, a beneficial owner of 10% or more of the outstanding shares of Common Stock (an “Interested Shareholder”) unless

The Articles provide that the “fair price” provision may be altered, amended or repealed only by the affirmative vote of the holders of at least 80% of the outstanding shares of Common Stock.

Statutory Limitation on “Significant Business Transactions”

General

The Washington BCA contains provisions that limit our ability to engage in “significant business transactions” with an “acquiring person”, each as defined below. We have no right to waive the applicability of these provisions.

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Significant Business Transactions Within Five Years of Share Acquisition Time

Subject to certain exceptions, for five years after an “acquiring person’s” “share acquisition time”, Avista may not engage in any “significant business transaction” with such “acquiring person” unless:

Significant Business Transactions More Than Five Years After Share Acquisition Time

Avista may not engage in certain “significant business transactions” (including mergers, share exchanges and consolidations) with any “acquiring person” unless:

Definitions

As used in this section:

“Significant business transaction” means any of various specified transactions involving an “acquiring person”, including:

“Acquiring person” means, with certain exceptions, a person (or group of persons) other than Avista or its subsidiaries who beneficially owns 10% or more of the outstanding Common Stock of Avista.

“Share acquisition time” means the time at which a person first becomes an “acquiring person” of Avista.

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Anti-Takeover Effect

Certain provisions of the Articles and the Bylaws described above under “Board of Directors” and the provisions of the Articles described above under “‘Fair Price’ Provision”, together with the provisions of the Washington BCA described above under “Statutory Limitations on ‘Significant Business Transactions’”, considered either individually or in the aggregate, may have an “anti-takeover” effect. These provisions could discourage a future takeover attempt which is not approved by Avista’s Board of Directors but which individual shareholders might deem to be in their best interests or in which shareholders would receive a premium for their shares over current market prices. As a result, shareholders who might desire to participate in such a transaction might not have an opportunity to do so.

Miscellaneous

The presently outstanding shares of Common Stock are fully paid and non-assessable. Upon issuance as contemplated by this prospectus and the applicable prospectus supplement, additional shares of Common Stock will be fully paid and nonassessable. The holders of shares of Common Stock are not and will not be subject to liability for further calls or assessment by, or for liabilities of, Avista.

The outstanding shares of Common Stock are listed on the New York Stock Exchange under the symbol “AVA”. Any new shares of Common Stock will also be listed on that Exchange subject to official notice of issuance.

The Transfer Agent and Registrar for the Common Stock is Computershare Shareowner Services LLC, 480 Washington Boulevard, 29^th Floor, Jersey City, New Jersey 07310.

WHERE YOU CAN FIND MORE INFORMATION

General

Avista is subject to the informational reporting requirements of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). Avista files annual, quarterly and current reports, proxy statements and other documents with the SEC (File No. 1-3701). These documents contain important business and financial information. You may read and copy any materials Avista files with the SEC at the SEC’s public reference room at 100 F Street, N.E., Washington, D.C. 20549. Please call the SEC at 1-800-SEC-0330 for further information on the public reference room. Avista’s SEC filings are also available to the public from the SEC’s website at http://www.sec.gov. Other than those documents or portions of documents incorporated by reference into this prospectus, information on this website does not constitute a part of this prospectus.

Incorporation of Documents by Reference

The SEC allows us to incorporate by reference the information that we file with the SEC. This allows us to disclose important information to you by referring you to those documents rather than repeating them in full in this prospectus. We are incorporating into this prospectus by reference:

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and all of those documents are deemed to be a part of this prospectus from the date of filing such documents; it being understood that documents which are “furnished” but not “filed”, in accordance with SEC rules, will not be deemed to be incorporated by reference. We refer to the documents incorporated into this prospectus by reference as the “Incorporated Documents”. Any statement contained in an Incorporated Document may be modified or superseded by a statement in this prospectus or any prospectus supplement (if such Incorporated Document was filed prior to the date of this prospectus) or such prospectus supplement, as the case may be, in any prospectus supplement or in any subsequently filed Incorporated Document. The Incorporated Documents as of the date of this prospectus are:

You may request copies of any of these filings, at no cost, by contacting us at the address or telephone number provided on page 2 of this prospectus. Avista maintains an Internet site at http://www.avistacorp.com which contains information concerning Avista and its affiliates. The information at or accessible through Avista’s Internet site is not incorporated in this prospectus by references and you should not consider it a part of this prospectus.

LEGAL MATTERS

The validity of the Securities and certain other matters will be passed upon for Avista by Marian M. Durkin, Esq., Senior Vice President, General Counsel and Chief Compliance Officer of Avista, and Pillsbury Winthrop Shaw Pittman LLP, counsel to Avista. Certain matters will be passed upon for any underwriters or agents by counsel to the extent identified in the applicable prospectus supplement. In giving their opinions, Pillsbury Winthrop Shaw Pittman LLP and counsel for any underwriters or agents may rely as to matters of Washington, Idaho, Montana and Oregon law upon the opinion of Marian M. Durkin, Esq.

EXPERTS

The consolidated financial statements incorporated in this prospectus by reference from Avista’s Annual Report on Form 10-K, and the effectiveness of Avista’s internal control over financial reporting have been audited by Deloitte & Touche LLP, an independent registered public accounting firm, as stated in their reports which are incorporated herein by reference. Such consolidated financial statements have been so incorporated in reliance upon the reports of such firm given upon their authority as experts in accounting and auditing.

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$375,000,000

Avista Corporation

First Mortgage Bonds, 4.35% Series due 2048

PROSPECTUS SUPPLEMENT

May 15, 2018

Joint Book-Running Managers

Co-Managers