UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

FORM 8-K

CURRENT REPORT PURSUANT
TO SECTION 13 OR 15(D) OF THE
SECURITIES EXCHANGE ACT OF 1934

Date of report (Date of earliest event reported) June 29, 2010

Affiliated Managers Group, Inc.

(Exact Name of Registrant as Specified in Its Charter)

Delaware

(State or Other Jurisdiction of Incorporation)

(617) 747-3300

(Registrant’s Telephone Number, Including Area Code)

N/A

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

o            Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

o            Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

o            Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

o            Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

ITEM 2.01                                       Completion of Acquisition or Disposition of Assets.

On June 30, 2010, Affiliated Managers Group, Inc. (“AMG”) completed its previously announced acquisition of the interests of Russell Investments (“Russell”) in Pantheon Ventures Inc., Pantheon Holdings Limited and Pantheon Capital (Asia) Limited (collectively, “Pantheon”).  Pantheon is a manager of regional funds-of-funds in Europe, the United States and Asia, as well as global secondary funds-of-funds, global infrastructure fund-of-funds and customized separate account programs.  In exchange for its interests in Pantheon, Russell received approximately $700,000,000 in cash at closing, subject to a working capital adjustment and post-closing true-up mechanism.  The acquisition was completed pursuant to the Purchase and Sale Agreement, dated as of February 10, 2010, as amended, by and among AMG, Frank Russell Company and, for limited purposes, Northwestern Mutual Life Insurance Company (of which Russell is a subsidiary), the terms and conditions of which are described in Item 1.01 of AMG’s Current Report on Form 8-K filed February 17, 2010, which description is incorporated by reference herein.  AMG financed the acquisition through borrowings under its credit facility and, as more fully described below, approximately $100,000,000 of proceeds from the partial settlement of forward sales of its common stock.

ITEM 7.01                                       Regulation FD Disclosure.

On June 30, 2010, AMG issued a press release announcing the completion of the acquisition.  A copy of the press release is furnished as Exhibit 99.1 to this Current Report on Form 8-K.

ITEM 8.01                                       Other Events.

AMG partially settled certain forward sales of its common stock made pursuant to the Confirmation Letter Agreement dated March 12, 2009, as amended, and the Confirmation Letter Agreement dated May 1, 2009 entered into by AMG and Bank of America, N.A., as forward purchaser (“BofA”), by issuing and delivering to BofA an aggregate of 1,799,111 shares of its common stock.  In connection with the partial settlements, AMG received approximately $100,000,000 in proceeds from BofA, which amounts AMG used to finance a portion of the acquisition.

ITEM 9.01                                       Financial Statements and Exhibits.

(a)                                  Financial Statements of Businesses Acquired

Financial statements required to be filed by this Item will be filed with the SEC as soon as practicable, but not later than 71 calendar days after the date on which this Current Report on Form 8-K is required to be filed.

(b)                                 Pro Forma Financial Information

Financial statements required to be filed by this Item will be filed with the SEC as soon as practicable, but not later than 71 calendar days after the date on which this Current Report on Form 8-K is required to be filed.

2

(d)                                 Exhibits

*  This exhibit shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, or otherwise subject to the liability of that section, nor shall it be incorporated by reference into any filing under the Securities Act of 1933 or the Securities Exchange Act of 1934.

3

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

4

EXHIBIT INDEX

*  This exhibit shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, or otherwise subject to the liability of that section, nor shall it be incorporated by reference into any filing under the Securities Act of 1933 or the Securities Exchange Act of 1934.

5

Exhibit 5.1

June 29, 2010

Affiliated Managers Group, Inc.

600 Hale Street

Prides Crossing, MA 01965-1000

Ladies and Gentlemen:

Reference is made to our opinion dated December 12, 2007 and included as Exhibit 5.1 to the registration statement on Form S-3 (File No. 333-148029) (the “Registration Statement”), filed by Affiliated Managers Group, Inc. (the “Company”), as of December 12, 2007, with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Securities Act”), relating to the registration under the Securities Act and the proposed issuance and sale from time to time pursuant to Rule 415 under the Securities Act of shares of the Company’s common stock, $0.01 par value per share (the “Common Stock”).  We are rendering this supplemental opinion in connection with the Company’s proposed issuance and delivery of shares of Common Stock (the “Shares”) from time to time, in settlement of, and pursuant to, the Confirmation Letter Agreement dated May 7, 2008, between the Company and Bank of America, N.A., as forward purchaser (“BofA”) (the “May 2008 Confirmation”), the Confirmation Letter Agreement dated May 1, 2009 between the Company and BofA, as forward purchaser (the “May 2009 Confirmation”), and the Confirmation Letter Agreement dated July 31, 2009, between the Company and Deutsche Bank AG, London Branch, as forward purchaser (“DB”) (the “July Confirmation”, and together with the May 2008 Confirmation, the May 2009 Confirmation and any subsequent related Confirmation Letter Agreements entered into with BofA or DB on substantially the same terms, the “Confirmations”).

In connection with this opinion, we have examined and relied upon such documents, records, certificates and other instruments as we have deemed necessary.  The opinions expressed below are limited to the Delaware General Corporation Law, including the reported cases interpreting that law.

Based upon the foregoing, we are of the opinion that, when issued and delivered in conformity with the authorizing resolutions of the Company’s Board of Directors dated April 2, 2008, April 21, 2009, and July 21, 2009 and the authorizing resolutions of the Pricing Committee of the Board of Directors dated May 7, 2008, August 15, 2008, February 3, 2009, May 1, 2009, and July 31, 2009, and against payment of the purchase price therefor in accordance with the Confirmations and as contemplated by the Registration Statement and any applicable prospectus, the Shares will be validly issued, fully paid and nonassessable.

We hereby consent to the filing of this opinion as an exhibit to the Company’s Current Report on Form 8-K.  In giving such consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act.

2

Exhibit 99.1

AMG Completes Investment in Private Equity Fund-of-Funds Manager Pantheon

BOSTON, June 30, 2010 - Affiliated Managers Group, Inc. (NYSE: AMG) today announced the completion of the acquisition of Pantheon from Russell Investments, a subsidiary of Northwestern Mutual Life Insurance Company.

Pantheon is a leading global private equity fund-of-funds manager, delivering private equity investment solutions to a broad range of clients for over 25 years.  Pantheon manages regional funds-of-funds in Europe, the United States and Asia, as well as global secondary funds-of-funds, global infrastructure fund-of-funds and customized separate account programs.  Pantheon currently has committed funds under management of approximately $26 billion across 300 global clients, including pension funds, endowments, government bodies and insurance companies.  The firm has experienced high client retention throughout its history, reflecting its strong performance over different economic cycles and high standards of client service.  With a team of 64 investment professionals (and a total staff of 140) in offices located in London, San Francisco, New York and Hong Kong, Pantheon is well-equipped to invest and serve clients worldwide.

In the Pantheon transaction, AMG purchased a majority equity interest, while the Pantheon management team acquired the remaining equity interest.  Pantheon management will continue to direct the firm’s day-to-day operations.

About Affiliated Managers Group

AMG is a global asset management company with equity investments in leading boutique investment management firms.  AMG’s innovative partnership approach allows each Affiliate’s management team to own significant equity in their firm while maintaining operational autonomy.  AMG’s strategy is to generate growth through the internal growth of existing Affiliates, as well as through investments in new Affiliates.  In addition, AMG provides centralized assistance to its Affiliates in strategic matters, marketing, distribution, product development and operations.  As of March 31, 2010, the aggregate assets under management of AMG’s Affiliates were approximately $260 billion in more than 350 investment products across a broad range of investment styles, asset classes and distribution channels.  For more information, please visit the Company’s website at www.amg.com.

Certain matters discussed in this press release may constitute forward-looking statements within the meaning of the federal securities laws.  Actual results and the timing of certain events could differ materially from those projected in or contemplated by the forward-looking statements due to a number of factors, including changes in the securities or financial markets or in general economic conditions, the availability of equity and debt financing, competition for acquisitions of interests in investment management firms, the ability to close pending investments, the investment performance of our Affiliates and their ability to effectively market their investment strategies, and other risks detailed from time to time in AMG’s filings with the Securities and Exchange Commission.  Reference is hereby made to the “Cautionary Statements” set forth in the Company’s Form 10-K for the year ended December 31, 2009.

AMG routinely posts information that may be significant for investors in the Investor Information section of its website, and encourages investors to consult that section regularly.  For additional information, please visit www.amg.com.

###