"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.

American Authors, formerly known as the Blue Pages, are an American rock band originally from Boston, now based in New York City, signed to Island Records. The band consists of lead vocalist and guitarist Zac Barnett, bassist Dave Rublin, and drummer Matt Sanchez. Former member includes guitarist and banjoist James Adam Shelley. They are best known for their hit singles "Believer" and "Best Day of My Life", from their debut album, Oh, What a Life, as well as their top 20 hit "Go Big or Go Home", from their second album, What We Live For.