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) 11/13/2008
	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	11/13/2008		P		57,131	A	$3.3552	15,051,590(3)	I	See Footnote(1)
Common Stock	11/14/2008		P		12,145	A	$3.4279	15,051,590(3)	I	See Footnote(2)

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 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)

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)

Explanation of Responses:

1. Open market purchase of 56,379 shares of the Issuer's Common Stock by Atlas Venture Fund V, L.P ("Atlas V") and of 752 shares 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. Open market purchase of 11,985 shares of the Issuer's Common Stock by Atlas V and of 160 shares 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.

3. Represents aggregate shares beneficially owned after all of the reported transactions. Includes 14,853,543 shares held directly by Atlas V and 198,047 shares held directly by AVE V. Each of the Filing Persons disclaims beneficial ownership of such shares except to the extent of its pecuniary interest therein.

	(See signatures included in Exhibit 99)	11/17/2008
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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