Sarah Ellen Polley OC (born January 8, 1979) is a Canadian filmmaker, political activist and retired actress. She first garnered attention as a child actress for her role as Ramona Quimby in the television series Ramona, based on Beverly Cleary's books. This subsequently led to her role as Sara Stanley in the Canadian television series Road to Avonlea (1990–1996). She has starred in many feature films, including The Adventures of Baron Munchausen (1988), Exotica (1994), The Sweet Hereafter (1997), Guinevere (1999), Go (1999), The Weight of Water (2000), No Such Thing (2001), My Life Without Me (2003), Dawn of the Dead (2004), Splice (2009), and Mr. Nobody (2009).

Polley made her feature film directorial debut with Away from Her (2006), for which she won the Canadian Screen Award for Best Director and was nominated for the Academy Award for Best Adapted Screenplay. Polley's second film, Take This Waltz (2011), premiered at the 2011 Toronto International Film Festival, followed by her first documentary film, Stories We Tell (2012). She also wrote the miniseries Alias Grace, based on the 1996 novel of the same name by Margaret Atwood. In 2022, Polley wrote and directed the film Women Talking, based on the 2018 novel of the same name by Miriam Toews, for which she won the Academy Award for Best Adapted Screenplay.