"So Yesterday" is a song by American singer Hilary Duff for her second studio album, Metamorphosis (2003). It was written and produced by The Matrix (a production team consisting of Lauren Christy, Scott Spock and Graham Edwards), with additional writing from Charlie Midnight. The song is influenced by pop rock music, and the lyrics chronicle the protagonist getting over a breakup with her boyfriend, declaring him as "so yesterday". The song received mixed to positive reviews from music critics, with some of them noting its close similarity to Avril Lavigne's works, while others named it one of Duff's best songs.