William S. Root (December 12, 1923 – March 18, 2002) was an American professional bridge player, teacher, and writer. He was from Boca Raton, Florida. Root was inducted into the ACBL Hall of Fame in 1997. The American Contract Bridge League observed in his citation, "Root was perhaps the best known bridge teacher in the world – and has probably taught the game to more people than anyone in history."