"Best Day of My Life" is a song by American pop rock band American Authors, released on March 19, 2013 by Mercury Records and Island Records as the lead single from their third extended play, American Authors (2013), and the second single from their debut studio album, Oh, What a Life (2014). The song was written by band members Zac Barnett, Dave Rublin, Matt Sanchez, and James Adam Shelley, along with producers Aaron Accetta and Shep Goodman.