Affiliated Managers Group Inc. is an American international investment management company headquartered in Massachusetts that owns stakes in a number of boutique asset management, hedge fund, and specialized private equity firms.

Founded in December 1993 by William J. Nutt as a privately owned company, its initial public offering on the New York Stock Exchange occurred in November 1997. Since 1997, AMG has grown to approximately $625 billion in assets under management with stakes in 29 money management firms including some of the best-known alternative investment financial management shops.,

When purchasing companies, AMG seldom buys 100% of a business. They typically allow the employees of the purchased company to retain a quarter to a half of the company, in an attempt to provide them with an incentive to maximize profit. On rare occasions, they will only purchase a minority share in a company. AMG purchased a 5 percent share in Value Partners Group Ltd. in 2009. The company, a Chinese asset manager, was AMG's first investment in China.

A substantial majority of Aston Asset Management, LP, was acquired by AMG on April 15, 2010.

In the 1990s, AMG focused on purchasing midsize money management companies. In a shift of strategy in 1997, they purchased the large mutual fund company Tweedy, Browne for $300 million. In 2010, AMG purchased Pantheon Ventures. Pantheon, a British private equity company, was AMG's largest acquisition since 1993. The company sold for $775 million. That year, AMG also purchased Artemis Investment Management LLP for $400 million.

Sean M. Healey was appointed chairman in October 2010, served as president and CEO since May 2001 and in other senior management positions since 1995. Healey received compensation of $14.9 million in 2011 and has an estimated net worth in excess of $100 million. Prior to joining AMG Healey was a vice president in the Mergers and Acquisitions Department at Goldman, Sachs & Co. and is a graduate of Harvard Law School (1987) and Harvard University (1983). Healey, the husband of former Massachusetts Lieutenant Governor Kerry Healey, is an advisory board member for the Harvard Law School Center on Lawyers and the Legal Profession, and serves as co-chair of the Peabody Essex Museum with AMG board member Samuel T. Byrne.

Nathaniel Dalton was named president and chief operating officer of AMG in January 2011 after serving as general counsel from 1996 to 2002 and then executive vice president responsible for affiliate development from 2002 through 2010. Prior to joining AMG Dalton was an attorney with the Goodwin Procter law firm where he represented AMG at its formation. Dalton received a J.D. from Boston University School of Law and a B.A. from the University of Pennsylvania. Dalton is the president and founder of the Guard Support of Massachusetts, a non-profit service organization supporting the families of National Guard troops.

As of 2017 Affiliated Managers Group shares are mainly held by institutional holdings (The Vanguard Group, BlackRock, State Street Corporation and others)