"A Day in the Life" is a song by the English rock band the Beatles that was released as the final track of their 1967 album Sgt. Pepper's Lonely Hearts Club Band. Credited to Lennon–McCartney, the opening and closing sections of the song were mainly written by John Lennon, with Paul McCartney primarily contributing the song's middle section. All four Beatles shaped the final arrangement of the song.

According to author Ian MacDonald, "A Day in the Life" was strongly influenced by Lennon's LSD-inspired revelations, this experience contributed to the Beatles willingness to experiment on Sgt. Pepper and to Lennon and McCartney returning to a level of collaboration that had been somewhat absent.