One

The Edge was playing chord progressions alone on an acoustic guitar in Hansa Studios when U2 found the song that saved their album. The band had been jamming on "Sick Puppy", an early version of "Mysterious Ways", and trying different progressions for the bridge. At the suggestion of producer Daniel Lanois, the Edge played two separate sections sequentially, and the group liked the way it flowed. They decided to play it together, and the guitarist later recalled that suddenly something very powerful was happening in the room. Bono said the melody and structure were done in 15 minutes. The track became "One", the third single from Achtung Baby, released on 24 February 1992.

The improvisation came at a tense moment. Sessions in Berlin, begun in October 1990 on the eve of German reunification, had been marked by conflict over the band's musical direction, and drummer Larry Mullen Jr. said he thought this might be the end. Bono's lyrics drew on the members' fractured relationships and his scepticism of the hippie idea of "oneness". He later declined an invitation to a festival called Oneness by sending a note to the Dalai Lama that borrowed a line from the song: "One, but not the same".

Brian Eno, reviewing session tapes, initially said "One" was the one track he despised, feeling it needed deconstruction. His own mix helped the band settle on an arrangement, and the final mix was completed at Windmill Lane Studios in September 1991.