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

Williams came to prominence for her roles in films such as Crazy Couple (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 television film Adam (1983) and the television miniseries Baby M (1988). Her third nomination was for a guest appearance on 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 appeared in the television series The Client (1995–96) and had recurring roles on the television series Dexter (2007) and Private Practice (2009–11).

In 2009 she began serving as president of the Screen Actors Guild Foundation; she is the foundation's honorary president. She has also had numerous guest roles on television and has appeared in several television films.