"Best Day of My Life" is a song by American indie rock band American Authors. 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. "Best Day of My Life" was originally recorded for release as a single by Mercury Records and Island Records on March 19, 2013, and later appeared as the second track on the band's third extended play American Authors (2013) and the third track on their debut studio album, Oh, What a Life (2014).

Zac Barnett told an interviewer for Blueprint Magazine, "Recently we have been experimenting with a lot of different instruments including banjo, mandolin and various percussion toys. Africa-influenced rhythms have been taking more of a prominent role in our songs which has then opened up our ideas on melodies. We're always open to trying new things and we get very excited to learn new instruments and experiment with new sounds. ... "Best Day of My Life" was an idea that James and I had been messing around with. We had the pre-chorus and chorus but once we showed the idea to the rest of the guys they came in and restructured the verses and added the stuttered "life" chorus. Looking back on it, the song changed a lot from the initial idea but that's what I love so much about it. I'll always remember that song being started on acoustic guitars in my tiny Bushwick bedroom, but all of us together as a band really took the song to a completely different place."

(Barnett mentions "the stuttered 'life' chorus"—as in "the best day of my li-i-i-i-ife"; the "stuttering" also occurs in a recurrent "whoa-oh-oh-oh-oh-oh-oh"—by which he refers to a lyrical tradition of stuttering in rock music, popularized by Buddy Holly,David Bowie ("Ch-Ch-Changes"),Elton John, and others.)

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