Mischa Anne Marsden Barton, (born 24 January 1986) is a British-American film, television, and stage actress, perhaps best known for her role as Marissa Cooper in the American television series The O.C.

When asked in interviews if she feels English or American, she states she feels English.

Mischa Barton was born in London, England, to an Irish mother, Nuala (née Quinn), a photographer, and an English father, Paul Marsden Barton, a foreign exchange broker. She has two sisters, younger Hania and elder Zoe, a barrister in London. Barton moved to New York City at the age of five and became a naturalised citizen of the United States in Los Angeles on 3 February 2006. Barton graduated from the Professional Children's School in Manhattan in 2004, and took a summer short course called Acting Shakespeare at The Royal Academy of Dramatic Art in June and July 2006, at Sir Richard Attenborough's urging, after he directed her in Closing the Ring.