"One After 909" is a song by the English rock band the Beatles from their 1970 album Let It Be. It was written by John Lennon, with input from Paul McCartney, and credited to their joint partnership. The album version is the live performance from the rooftop concert which took place on 30 January 1969. This performance is also included in the Let It Be film. The song was written no later than spring 1960 and perhaps as early as 1957, and is one of the first Lennon–McCartney compositions. "One After 909" is perhaps more reminiscent of early American rock and roll than any of the other songs from the rooftop show, and as a joke for the rooftop chatter, Lennon sings a variant on the opening line of "Danny Boy" after the song is finished.

Let It Be is the twelfth and final studio album by the English rock band the Beatles. It was released on 8 May 1970, almost a month after the group's public break-up, in tandem with the documentary of the same title. Concerned about recent friction within the band, Paul McCartney had conceived the project as an attempt to reinvigorate the group by returning to simpler rock 'n' roll configurations. Its rehearsals started at Twickenham Film Studios on 2 January 1969 as part of a planned television documentary showing the Beatles' return to live performance.