Mischa Anne Marsden Barton (born 24 January 1986) is a British-American film, television, and stage actress. She began her career onstage, appearing in Tony Kushner's Slavs! and took the lead in James Lapine's Twelve Dreams at New York City's Lincoln Center. She made her screen debut with a guest appearance on the American soap opera All My Children (1995) and voicing Betty Ann Bongo on the Nickelodeon cartoon series KaBlam! (1996–97). Her first significant film role was as the protagonist of Lawn Dogs (1997), a drama co-starring Sam Rockwell. She appeared in major pictures such as the romantic comedy Notting Hill (1999) and M. Night Shyamalan's psychological thriller The Sixth Sense (1999). She also starred in the indie crime drama Pups (1999).

Barton later appeared in the independent drama Lost and Delirious (2001) and guest-starred as Evan Rachel Wood's girlfriend on ABC's Once and Again (2001–02). She played Marissa Cooper in the Fox television series The O.C.(2003–2006), for which she received two Teen Choice Awards. The role brought Barton into mainstream fame, and Entertainment Weekly named her the "It Girl" of 2003.