SEC Form 3

FORM 3

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

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1. Name and Address of Reporting Person* Atlas Venture Fund VIII, L.P. (Last) (First) (Middle) 56 WAREHAM STREET, FLOOR 3 (Street) BOSTON MA 02118 (City) (State) (Zip)	2. Date of Event Requiring Statement (Month/Day/Year) 06/29/2021	3. Issuer Name and Ticker or Trading Symbol INTEGRAL AD SCIENCE HOLDING CORP. [ IAS ]
		4. Relationship of Reporting Person(s) to Issuer (Check all applicable) Director X 10% Owner Officer (give title below) Other (specify below)	5. 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 Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)
Common stock, $0.001 par value	22,722,770	I	See Footnote(1)

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

1. Name and Address of Reporting Person* Atlas Venture Fund VIII, L.P. (Last) (First) (Middle) 56 WAREHAM STREET, FLOOR 3 (Street) BOSTON MA 02118 (City) (State) (Zip)

1. Name and Address of Reporting Person* Atlas Venture Associates VIII, L.P. (Last) (First) (Middle) 56 WAREHAM STREET, FLOOR 3 (Street) BOSTON MA 02118 (City) (State) (Zip)

1. Name and Address of Reporting Person* Atlas Venture Associates VIII, Inc. (Last) (First) (Middle) 56 WAREHAM STREET, FLOOR 3 (Street) BOSTON MA 02118 (City) (State) (Zip)

Explanation of Responses:

1. Includes 22,722,770 shares held directly by Atlas Venture Fund VIII, L.P. ("Atlas VIII"). Atlas Venture Associates VIII, L.P. ("AVA VIII LP") is the sole general partner of Atlas VIII. Atlas Venture Associates VIII, Inc. ("AVA VIII Inc.") is the sole general partner of AVA VIII LP. Each of Atlas VIII, AVAI VIII LP and AVA VIII Inc. disclaim beneficial ownership of all shares except to the extent of its pecuniary interest, if any, therein. This report shall not be deemed to be an admission that the reporting persons are the beneficial owners of such securities for purposes of Section 16 or for any other purpose.

Remarks:

	Atlas Venture Fund VIII, L.P., By: Atlas Venture Associates VIII, L.P., its general partner, By: Atlas Venture Associates VIII, Inc., its general partner, By: Frank Castellucci, General Counsel and Secretary /s/ Frank Castellucci	06/29/2021
	Atlas Venture Associates VIII, L.P. By: Atlas Venture Associates VIII, Inc., its general partner, By: Frank Castellucci, General Counsel and Secretary /s/ Frank Castellucci	06/29/2021
	Atlas Venture Associates VIII, Inc, By: Frank Castellucci, General Counsel and Secretary /s/ Frank Castellucci	06/29/2021
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 5 (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).
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