FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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(Print or Type Responses)

1. Name and Address of Reporting Person * FLORANCE ANDREW C   2. Issuer Name and Ticker or Trading Symbol COSTAR GROUP INC [CSGP] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) __X__ Director _____ 10% Owner __X__ Officer (give title below) _____ Other (specify below) President and CEO (Last) (First) (Middle) C/O COSTAR GROUP, INC., 1331 L STREET, NW 3. Date of Earliest Transaction (Month/Day/Year) 07/29/2013 (Street) WASHINGTON, DC 20005 4. If Amendment, Date Original Filed(Month/Day/Year) 6. Individual or Joint/Group Filing(Check Applicable Line) _X_ Form filed by One Reporting Person ___ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned

1.Title of Security (Instr. 3) 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock, par value $0.01 per share 07/29/2013   M   4,000 A $ 25 293,196 (1) D   Common Stock, par value $0.01 per share 07/29/2013   M   37,374 A $ 51.92 330,570 (2) D   Common Stock, par value $0.01 per share 07/29/2013   S   37,374 D $ 155.86 (3) 293,196 (1) D   Common Stock, par value $0.01 per share 07/29/2013   M   4,234 A $ 43.99 297,430 (4) D   Common Stock, par value $0.01 per share 07/29/2013   S   4,234 D $ 157 293,196 (1) D   Common Stock, par value $0.01 per share 07/30/2013   M   30,520 A $ 43.99 323,716 (5) D   Common Stock, par value $0.01 per share 07/30/2013   S   30,520 D $ 157.03 (6) 293,196 (1) D

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 3)

2. Conversion or Exercise Price of Derivative Security

3. Transaction Date (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

4. Transaction Code (Instr. 8)

5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5)

6. Date Exercisable and Expiration Date (Month/Day/Year)

7. Title and Amount of Underlying Securities (Instr. 3 and 4)

8. Price of Derivative Security (Instr. 5)

9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)

10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)

11. Nature of Indirect Beneficial Ownership (Instr. 4)

Code

V

(A)

(D)

Date Exercisable

Expiration Date

Title

Amount or Number of Shares

Option to Acquire Common Stock

$ 25

07/29/2013

M

4,000

(7)

03/01/2019

Common Stock

4,000

$ 0

54,400

D

Option to Acquire Common Stock

$ 51.92

07/29/2013

M

37,374

(8)

12/11/2016

Common Stock

37,374

$ 0

1,926

D

Option to Acquire Common Stock

$ 43.99

07/29/2013

M

4,234

(9)

02/26/2018

Common Stock

4,234

$ 0

35,066

D

Option to Acquire Common Stock

$ 43.99

07/30/2013

M

30,520

(9)

02/26/2018

Common Stock

30,520

$ 0

4,546

D

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
FLORANCE ANDREW C C/O COSTAR GROUP, INC. 1331 L STREET, NW WASHINGTON, DC 20005	X		President and CEO

Signatures

/s/ Jonathan Coleman, Attorney-in-Fact		07/31/2013
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	Represents all shares of Common Stock owned, consisting of 91,562 shares of Common Stock and 201,634 shares of Common Stock subject to unvested Restricted Stock Grants.
(2)	Represents all shares of Common Stock owned, consisting of 128,936 shares of Common Stock and 201,634 shares of Common Stock subject to unvested Restricted Stock Grants.
(3)	Average based on sales prices ranging from $155.00 to $158.88.
(4)	Represents all shares of Common Stock owned, consisting of 95,796 shares of Common Stock and 201,634 shares of Common Stock subject to unvested Restricted Stock Grants.
(5)	Represents all shares of Common Stock owned, consisting of 122,082 shares of Common Stock and 201,634 shares of Common Stock subject to unvested Restricted Stock Grants.
(6)	Average based on sales prices ranging from $157.00 to $157.26.
(7)	The option vested in three equal installments on March 2, 2010, March 2, 2011 and March 2, 2012.
(8)	The option vested in three equal installments on December 12, 2007, December 12, 2008 and December 12, 2009.
(9)	The option vested in three equal installments on February 27, 2009, February 27, 2010 and February 27, 2011.

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