“Once” is the first track on the band’s debut album, Ten, released on August 27, 1991. On Ten, it is preceded by a brief interlude of the album’s closing hidden track, “Master/Slave.” Besides Ten, the song was also featured as a B-side on the single for “Alive.” Remixed versions of the song were included on Pearl Jam’s 2004 greatest hits album, Rearviewmirror, and the 2009 Ten reissue.

The song is the middle chapter of a trilogy of songs in what Vedder later described as a mini-opera entitled Mamasan, with it being preceded by “Alive” and followed by “Footsteps.” “Once” tells the tale of a man’s descent into madness which leads him into becoming a serial killer.