Marsha Mason (born April 3, 1942) is an American actress. Born in St. Louis, Missouri, she was married to playwright and screenwriter Neil Simon, and starred in several movies based on his works, including The Goodbye Girl, Chapter Two, Only When I Laugh, The Cheap Detective and Max Dugan Returns. Chapter Two, in fact, was based on her relationship with Simon.

She was nominated for the Academy Award for Best Actress for Cinderella Liberty, The Goodbye Girl, Chapter Two and Only When I Laugh.

In 2001 she opened an herbal medicine shop, selling products from the garden of her home in Abiquiu, New Mexico.