William Wakefield Baum (born November 21, 1926) is an American clergyman of the Roman Catholic Church. He served as Bishop of Springfield-Cape Girardeau (1970-1973) and Archbishop of Washington (1973-1980) before serving in the Roman Curia as Prefect of the Congregation for Catholic Education (1980-1990) and Major Penitentiary (1990-2001). He was elevated to the cardinalate in 1976, and is currently the longest-serving cardinal from the United States.