Margaret JoBeth Williams (born December 6, 1948) is an American actress and director, and current President of the Screen Actors Guild Foundation.

Williams rose to prominence appearing in such films as Stir Crazy (1980), Poltergeist (1982), The Big Chill (1983), The Day After (1983), Teachers (1984), and Poltergeist II: The Other Side (1986). A three-time Emmy Award nominee, she was nominated for Outstanding Lead Actress in a Miniseries or a Movie for her work in the TV movie Adam (1983) and the TV miniseries Baby M (1988). Her third nomination was for her guest role in the sitcom Frasier (1994).