William Paxson Purcell III (born October 25, 1953) is an American politician who served as the fifth mayor of the Metropolitan Government of Nashville and Davidson County, elected first in 1999 and reelected to a second term in 2003. He is a member of the Democratic Party. On June 24, 2008 he was named director of Harvard University's Institute of Politics (IOP) at the John F. Kennedy School of Government. Purcell assumed the post on September 1, 2008. He was one of three co-chairs of the Harvard University Allston Work Team. He is now in private practice of law in Nashville and an adjunct professor of Public Policy at Vanderbilt University.