“One” is a song by Irish rock band U2. It is the third track from their 1991 album Achtung Baby, and it was released as the record’s third single in March 1992. It was recorded at three recording studios, Hansa Ton Studios, Elsinore, and Windmill Lane Studios. During the album’s recording, conflict arose between the band members over the direction of U2’s sound and the quality of their material. Tensions almost prompted the band to break up, until guitarist The Edge composed a chord progression that inspired the group to improvise the song, which was written as a ballad. The band worked on the mix for “One” throughout the remainder of the album’s sessions. The lyrics, written by lead singer Bono, describe fracturing interpersonal relationships, but they have been interpreted in other ways.

“One” was released as a benefit single, with proceeds going towards AIDS research. The song reached number seven on the UK Singles Chart and number ten on the Billboard Hot 100, and it topped the US Billboard Album Rock Tracks and Modern Rock Tracks charts. In promotion of the song, the band had several music videos filmed, although they were not pleased until the third video was created.

The song has since been acclaimed as one of the greatest songs of all time, and it is consistently featured in listener and critic polls. The song has been played by U2 at every one of their tour concerts since the song’s live debut in 1992, and it has appeared in many of the band’s concert films. In a live setting, “One” is often used by the band to promote human rights or social justice causes, and the song lends its namesake to Bono’s charitable organization, the ONE Campaign. In 2006, U2 re-recorded the song as part of a duet with contemporary R&B singer Mary J. Blige.

Looking for some new inspiration, the guys wrapped up their tour, spent several months at home and headed to Berlin in October 1990, flying into town the day Germany officially reunited.

The city was joyous. While the Wall between East and West Berlin was falling down, though, new barriers were being built between U2’s four members. Bono and the Edge wanted to explore new sounds, with hip-hop, Madchester and club music serving as good places to start. Adam Clayton, the only one with any real nightclub experience, told the others they didn’t know the first thing about dance music. Meanwhile, Mullen balked at the drum machines that producers Brian Eno and Daniel Lanois had pulled into the studio. Wasn’t he supposed to be the band’s percussionist?

With U2’s future in doubt, “One” literally brought the band back together. Working one evening at Hansa Studios – ground zero for David Bowie’s groundbreaking work with Eno in the 1970s – the Edge began composing a bridge for the song that later became “Ultraviolet (Light My Way).” He banged out some minor chords on piano, then came up with a major-key resolution. When he switched over to acoustic guitar and starting playing the sections back-to-back, a new song was born. The other bandmates joined in, with Bono improvising some lyrics inspired by a recent invitation from the Dalai Lama, who’d invited the group to attend a festival called Oneness. Within minutes, the framework for “One” was complete.

On an album filled with irony, sex and self-deprecation, “One” cuts through to the heart of a relationship. Each verse poses new questions – Is it getting better? Did I disappoint you? Have you come here for forgiveness? – without offering any answers in return. Keeping things deliberately vague, Bono lobs his inquiries into thin air, aiming them at his band, his spouse, the Edge’s estranged wife, or maybe even none of the above. The addressees don’t matter. “One” isn’t about love, after all; it’s about resignation.

“The song is a bit twisted,” Bono explained in Neil McCormick’s U2 By U2, “which is why I could never figure out why people want it at their weddings. I have certainly met a hundred people who’ve had it at their weddings. I tell them, ‘Are you mad? It’s about splitting up!’”

But U2 didn’t split up. They tied up some loose ends in Berlin, flew back to Dublin and finished Achtung Baby, which reinvented the band’s sound, image and audience. The God-fearing boys who’d appeared so earnest, so unapologetically self-righteous during the Rattle And Hum days had grown into clever, comfortable men who could laugh at their own success. Bono even began hamming it up onstage in leather jackets and oversized sunglasses, finally embracing the “rockstar” persona that his job afforded. The rest of the band followed suit.

Still, “One” is Achtung Baby’s most vulnerable moment, the human heart that beats between the glitzy, industrial gloss of “Even Better Than The Real Thing” and “Until The End Of The World.” Bono sings the lyrics in a half-broken voice, sounding worn out and dejected until the last 30 seconds, where he flips into a gorgeous falsetto. The Edge, who ended “With Or Without You” with a simple guitar pattern instead of a traditional solo, does the same thing here, chiming his way around Bono’s vocals with ringing, slightly delayed quarter notes. The two parts support one another, perhaps taking their cues from the song’s own words (“We’re one, but we’re not the same / We get to carry each other”).

It may have been cooked up in a frenzied half-hour of inspiration, but “One” has enjoyed a long shelf life. Every U2 concert since 1992 has featured the song. Johnny Cash covered it on 2000’s American III: Solitary Man, and Mary J. Blige scored a hit six years later with her own version, which turned the tune’s fragility into an anthem of unity. Recently, “One” has also been linked to Bono’s work as a social activist, even lending its name to the ONE Campaign.

People tend to attribute U2’s success to an ability to adapt, change and reinvent, often one step ahead of the mainstream. “One” was the group’s first major transformation, the song that blasted through a decade’s worth of self-serious rock and roll and signaled something different. Other transformations followed, including an eventual return to the anthems that kicked off U2’s career. But without “One,” there’d be no Achtung Baby … and without Achtung Baby, there’d be no U2.