(1)

The aggregate number of shares to be registered is subject to adjustment by reason of stock splits, stock dividends and other events pursuant to the terms of the 2015 Biogen Employee Stock Purchase Plan (“ESPP”). Accordingly, pursuant to Rule 416 under the Securities Act of 1933, as amended (the “Securities Act”), this Registration Statement covers, in addition to the number of shares of common stock shown in the table above, an indeterminate number of shares of the Registrant’s common stock which may be subject to grant or otherwise issuable by operation of the provisions of the ESPP governing such adjustments.

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(2)	Estimated solely for the purpose of calculating the registration fee pursuant to Rule 457(h) under the Securities Act. The proposed maximum offering price per share and the proposed maximum aggregate offering price are based upon the average of the high ($415.99) and low ($410.27) sales price for Registrant’s common stock as reported on the NASDAQ Global Select Market on June 24, 2015.

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(a)	Biogen’s Annual Report on Form 10-K for the fiscal year ended December 31, 2014, filed on February 4, 2015;

(b)	Biogen’s Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2015, filed on April 24, 2015;

(c)	Biogen’s Current Report on Form 8-K filed on March 27, 2015; and

(d)	The description of Biogen’s common stock contained in the Registration Statement on Form 8-B filed on June 2, 1997, including any amendment or report updating such description of the common stock.

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(a)	The undersigned Registrant hereby undertakes:

(1)	To file, during any period in which offers or sales are being made, a post-effective amendment to this Registration Statement:

(i)	To include any prospectus required by Section 10(a)(3) of the Securities Act;

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(ii)

To reflect in the prospectus any facts or events arising after the effective date of the Registration Statement (or the most recent post-effective amendment thereof) which, individually or in the aggregate, represent a fundamental change in the information set forth in the Registration Statement. Notwithstanding the foregoing, any increase or decrease in volume of securities offered (if the total dollar value of securities offered would not exceed that which was registered) and any deviation from the low or high end of the estimated maximum offering range may be reflected in the form of a prospectus filed with the Commission pursuant to Rule 424(b) under the Securities Act if, in the aggregate, the changes in volume and price represent no more than a 20 percent change in the maximum aggregate offering price set forth in the “Calculation of Registration Fee” table in the effective registration statement;

(iii)	To include any material information with respect to the plan of distribution not previously disclosed in the Registration Statement or any material change to such information in the Registration Statement;

(2)	That, for the purpose of determining any liability under the Securities Act, each such post-effective amendment shall be deemed to be a new registration statement relating to the securities offered herein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(3)	To remove from registration by means of a post-effective amendment any of the securities being registered which remain unsold at the termination of the offering.

(b)

The undersigned Registrant hereby undertakes that, for purposes of determining any liability under the Securities Act, each filing of the Registrant’s annual report pursuant to Section 13(a) or 15(d) of the Exchange Act (and, where applicable, each filing of an employee benefit plan’s annual report pursuant to Section 15(d) of the Exchange Act) that is incorporated by reference in the Registration Statement shall be deemed to be a new Registration Statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(c)

Insofar as indemnification for liabilities arising under the Securities Act may be permitted to directors, officers and controlling persons of the Registrant pursuant to the provisions referred to in Item 6 hereof, or otherwise, the Registrant has been advised that in the opinion of the Commission such indemnification is against public policy as expressed in the Securities Act and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the Registrant of expenses incurred or paid by a director, officer or controlling person of the Registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the Registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Securities Act and will be governed by the final adjudication of such issue.

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