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).

Her directorial debut, the 1994 short film On Hope, earned her an Academy Award nomination for Best Live Action Short Film. She also starred in the TV series The Client (1995–96), and had recurring roles in the TV series Dexter (2007) and Private Practice (2009–11).

In 2009 she began serving as president of the Screen Actors Guild Foundation; she is President Emeritus of the foundation. She has also had numerous guest starring roles on TV and has starred in several TV movies.