SEC Form 4

FORM 4		UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940	OMB APPROVAL OMB Number: 3235-0287 Estimated average burden hours per response: 0.5
	Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

1. Name and Address of Reporting Person* ATLAS VENTURE FUND V LP (Last) (First) (Middle) C/O ATLAS VENTURE 890 WINTER STREET, SUITE 320 (Street) WALTHAM MA 02451 (City) (State) (Zip)	2. Issuer Name and Ticker or Trading Symbol Isilon Systems, Inc. [ ISLN ]	5. Relationship of Reporting Person(s) to Issuer (Check all applicable) Director X 10% Owner Officer (give title below) Other (specify below)
	3. Date of Earliest Transaction (Month/Day/Year) 08/04/2010
	4. If Amendment, Date of Original Filed (Month/Day/Year)	6. Individual or Joint/Group Filing (Check Applicable Line) Form filed by One Reporting Person X Form filed by More than One Reporting Person

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	08/04/2010		S		210,000(1)	D	$17.9443(2)	13,685,380	I	See Footnote(3)
Common Stock	08/05/2010		S		100,490(4)	D	$18.0159(5)	13,584,890	I	See Footnote(6)
Common Stock	08/06/2010		S		9,800(7)	D	$18.1164(8)	13,575,090	I	See Footnote(9)

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 Securities Underlying Derivative Security (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: 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

1. Name and Address of Reporting Person* ATLAS VENTURE FUND V LP (Last) (First) (Middle) C/O ATLAS VENTURE 890 WINTER STREET, SUITE 320 (Street) WALTHAM MA 02451 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* ATLAS VENTURE ASSOCIATES V LP (Last) (First) (Middle) C/O ATLAS VENTURE 890 WINTER STREET, SUITE 320 (Street) WALTHAM MA 02451 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* ATLAS VENTURE ENTREPRENEURS FUND V LP (Last) (First) (Middle) C/O ATLAS VENTURE 890 WINTER STREET, SUITE 320 (Street) WALTHAM MA 02451 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

Explanation of Responses:

1. Sale of 207,237 shares of the Issuer's Common Stock by Atlas Venture Fund V, L.P. ("Atlas V") and of 2,763 shares of the Issuer's Common Stock held by Atlas Venture Entrepreneurs' Fund V, L.P. ("AVE V"). These shares are owned directly by Atlas V and AVE V. Atlas Venture Associates V, L.P. is the general partner of Atlas V and AVE V. Each of the Filing Persons disclaims beneficial ownership of such shares except to the extent of its pecuniary interest therein.

2. Represents a weighted-average price of shares disposed. These shares were sold in multiple transactions at prices ranging from $17.73 to $18.18, inclusive. The reporting person undertakes to provide to the issuer, any security holder of the issuer, or the SEC staff, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth.

3. Represents aggregate shares beneficially owned after the reported transaction. Includes 13,505,309 shares held directly by Atlas V and 180,071 shares held directly by AVE V. These shares are owned directly by Atlas V and AVE V. Atlas Venture Associates V, L.P. is the general partner of Atlas V and AVE V. Each of the Filing Persons disclaims beneficial ownership of such shares except to the extent of its pecuniary interest therein.

4. Sale of 99,168 shares of the Issuer's Common Stock by Atlas V and of 1,322 shares of the Issuer's Common Stock held by AVE V. These shares are owned directly by Atlas V and AVE V. Atlas Venture Associates V, L.P. is the general partner of Atlas V and AVE V. Each of the Filing Persons disclaims beneficial ownership of such shares except to the extent of its pecuniary interest therein.

5. Represents a weighted-average price of shares disposed. These shares were sold in multiple transactions at prices ranging from $17.90 to $18.11, inclusive. The reporting person undertakes to provide to the issuer, any security holder of the issuer, or the SEC staff, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth.

6. Represents aggregate shares beneficially owned after the reported transaction. Includes 13,406,141 shares held directly by Atlas V and 178,749 shares held directly by AVE V. These shares are owned directly by Atlas V and AVE V. Atlas Venture Associates V, L.P. is the general partner of Atlas V and AVE V. Each of the Filing Persons disclaims beneficial ownership of such shares except to the extent of its pecuniary interest therein.

7. Sale of 9,671 shares of the Issuer's Common Stock by Atlas V and of 129 shares of the Issuer's Common Stock held by AVE V. These shares are owned directly by Atlas V and AVE V. Atlas Venture Associates V, L.P. is the general partner of Atlas V and AVE V. Each of the Filing Persons disclaims beneficial ownership of such shares except to the extent of its pecuniary interest therein.

8. Represents a weighted-average price of shares disposed. These shares were sold in multiple transactions at prices ranging from $18.00 to $18.17, inclusive. The reporting person undertakes to provide to the issuer, any security holder of the issuer, or the SEC staff, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth.

9. Represents aggregate shares beneficially owned after all of the reported transactions. Includes 13,396,470 shares held directly by Atlas V and 178,620 shares held directly by AVE V. These shares are owned directly by Atlas V and AVE V. Atlas Venture Associates V, L.P. is the general partner of Atlas V and AVE V. Each of the Filing Persons disclaims beneficial ownership of such shares except to the extent of its pecuniary interest therein.

Remarks:

This statement on Form 4 is filed by Atlas Venture Associates V, L.P., Atlas Venture Fund V, L.P., and Atlas Venture Entrepreneurs' Fund V, L.P. The principal business address of each of the reporting persons is 890 Winter Street, Suite 320, Waltham, Massachusetts 02451. The reporting persons disclaim beneficial ownership of the securities listed herein except to the extent of their pecuniary interest therein.

	Atlas Venture Fund V, L.P., By: Atlas Venture Associates V, L.P., Its General Partner, By: Atlas Venture Associates V, Inc., Its General Partner, By: /s/ Kristen Laguerre, Vice President	08/06/2010
	Atlas Venture Entrepreneurs' Fund V, L.P., By: Atlas Venture Associates V, L.P., Its General Partner, By: Atlas Venture Associates V, Inc., Its General Partner, By: /s/ Kristen Laguerre, Vice President	08/06/2010
	Atlas Venture Associates V, L.P., By: Atlas Venture Associates V, Inc., Its General Partner, By: /s/ Kristen Laguerre, Vice President	08/06/2010
	** Signature of Reporting Person	Date
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