Filed Pursuant to Rule 424(b)(3)
Registration No. 333-135417

PROSPECTUS SUPPLEMENT NO. 9
(TO PROSPECTUS DATED JUNE 28, 2006)

$291,000,000

AMG Capital Trust I

5.10% Convertible Trust Preferred Securities
(liquidation amount $50.00 per security)
guaranteed to the extent described herein by,
and convertible into the common stock of,

Affiliated Managers Group, Inc.


This document supplements the prospectus dated June 28, 2006 (the “Prospectus”) relating to resales by selling securityholders of the securities described in the Prospectus.

This Prospectus Supplement should be read in conjunction with, and is not complete without, and may not be delivered or utilized without, the Prospectus, including any amendments or supplements thereto.


Investing in these securities involves risk.  See “Risk Factors” beginning on page 10 of the Prospectus.

Neither the Securities and Exchange Commission nor any state securities regulators has approved or disapproved of these securities or passed upon the adequacy or accuracy of this Prospectus Supplement.  Any representation to the contrary is a criminal offense.


The information in the table appearing under the heading “Selling Securityholders,” beginning on page 81 of the Prospectus, is hereby amended by adding the information below with respect to securityholders not previously listed in the Prospectus (including in any amendments or supplements thereto), and with respect to securityholders previously listed in the Prospectus (including in any amendments or supplements thereto), by superseding the information about such securityholder with the information in the table below:

SELLING SECURITYHOLDERS

Selling Securityholder

 

Number of Trust Preferred
Securities Owned and
Offered

 

 

 

 

 

 

 

1976 Distribution Trust FBO A.R. Lauder

 

 

61

 

 

 

 

 

 

 

 

2000 Revocable Trust FBO A.R. Lauder

 

 

58

 

 

 

 

 

 

 

 

Advent Convertible Master Fund LP

 

 

178,472

 

 

 

 

 

 

 

 

Alcon Laboratories

 

 

5,036

 

 

 

 

 

 

 

 

Arlington County Employee Benefit System

 

 

7,367

 

 

 

 

 

 

 

 

AVK Fund

 

 

25,000

 

 

 

 

 

 

 

 

British Virgin Islands Social Security Board

 

 

1,701

 

 

 

 

 

 

 

 

City University of New York

 

 

1,475

 

 

 

 

 

 

 

 

Grady Hospital

 

 

1,408

 

 

 

 

 

 

 

 

HFR Convertible Arbitrage

 

 

11,277

 

 

 

 

 

 

 

 

Independence Blue Cross

 

 

8,782

 

 

 

 

 

 

 

 

Lyxor Convertible Arbitrage Fund

 

 

6,281

 

 

 

 

 

 

 

 

New Orleans Firefighters

 

 

861

 

 

 

 

 

 

 

 

Occidental Petroleum

 

 

3,274

 

 

 

 

 

 

 

 

Police and Firemen of the City of Detroit

 

 

6,136

 

 

 

 

 

 

 

 

ProMutual

 

 

9,298

 

 

 

 

 

 

 

 

San Francisco Public Employees Retirement System

 

 

14,561

 

 

 

 

 

 

 

 

Silvercreek II Limited

 

 

7,800

 

 

 

 

 

 

 

 

Silvercreek Limited Partnership

 

 

12,200

 

 

 

 

 

 

 

 

The Grable Foundation

 

 

969

 

 

 

 

 

 

 

 

Trustmark

 

 

4,013

 

 

 

The date of this prospectus supplement is October 5, 2006.