Page 1

Table of Contents ( Mark One ) X UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 FORM 10 - K For the fiscal year ended December 31 , 2020 OR TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from Commission File Number 001-13459 Delaware ( State or other jurisdiction of incorporation or organization ) AMG AFFILIATED MANAGERS GROUP , INC . ( Exact name of registrant as specified in its charter ) to Title of each class Common Stock ( $ 0.01 par value ) 5.875 % Junior Subordinated Notes due 2059 4.750 % Junior Subordinated Notes due 2060 777 South Flagler Drive , West Palm Beach , Florida , 33401 ( Address of principal executive offices ) 04-3218510 ( IRS Employer Identification Number ) ( 800 ) 345-1100 ( Registrant's telephone number , including area code ) Securities registered pursuant to Section 12 ( b ) of the Act : Trading Symbol ( s ) AMG MGR MGRB None Name of each exchange on which registered New York Stock Exchange New York Stock Exchange New York Stock Exchange Securities registered pursuant to Section 12 ( g ) of the Act :