Amanda Michelle Seyfried (pronounced /ˈsaɪfrɪd/ "sigh-frid"; born December 3, 1985) is an American actress and former child model. She is best known for her roles as Sophie Sheridan in the feature film Mamma Mia! and as Karen Smith in Mean Girls; she has also appeared in other feature films such as Alpha Dog and Jennifer's Body, and in the television shows Veronica Mars, Big Love, and House.

Amanda Seyfried was born in Allentown, Lehigh County, Pennsylvania, United States, the daughter of Ann, an occupational therapist, and Jack Seyfried, a pharmacist. Her sister, Jennifer Seyfried, is a musician in the Philadelphia organ-driven rock band Love City at MySpace. Amanda graduated in 2003 from Allentown's William Allen High School and subsequently enrolled at New York City's Fordham University. As a teenager, she appeared on the cover of three Francine Pascal books. She also sang "Thank You for the Music" at Michael Jackson's memorial concert.

Seyfried started her career as a model at age eleven. From there she went on to acting uncredited in the daytime drama Guiding Light. In 2000, she originated the role of Lucy Montgomery on As the World Turns. From 2002 to 2003, she played the role of Joni Stafford on ABC's All My Children.