U2 is an Irish rock band which formed in 1976 in Dublin, Ireland. Since the band’s formation, they have consisted of Bono, The Edge, Adam Clayton and Larry Mullen, Jr. The band is the biggest selling alternative rock act of all time, having sold 140 million albums worldwide as of 2008. They have won 22 Grammys and were inducted into the Rock & Roll Hall of Fame in 2005. As of 2009, they have released 12 albums and 58 singles.

The band formed at Mount Temple secondary school in 1976 when the members were teenagers with limited musical proficiency. Within four years, they signed to Island Records and released their debut album Boy. By the mid-1980s, they had become a top international act. They were more successful as a live act than they were at selling records, until their 1987 album The Joshua Tree, which, according to Rolling Stone, elevated the band's stature "from heroes to superstars".

Their 1991 album Achtung Baby and the accompanying Zoo TV Tour were a musical and thematic reinvention for the band. Reacting to their own sense of musical stagnation and a late-1980s critical backlash, U2 incorporated dance music and alternative rock influences into their sound and performances, abandoning their earnest image for a more ironic, self-deprecating tone. Similar experimentation continued for the remainder of the 1990s. Since 2000, U2 have pursued a more conventional sound, while maintaining influences from their previous musical explorations.

U2 have released 12 studio albums and are among the most critically and commercially successful groups in popular music. They have won 22 Grammy Awards,[3] more than any other band, and they have sold more than 150 million records. In 2005, the band were inducted into the Rock and Roll Hall of Fame in their first year of eligibility. Rolling Stone magazine listed U2 at number 22 in its list of the "100 Greatest Artists of All Time". Throughout their career, as a band and as individuals, they have campaigned for human rights and philanthropic causes, including Amnesty International, the ONE/DATA campaigns, Product Red, and The Edge's Music Rising.

Since their inception, U2 have developed and maintained a distinctly recognisable sound, with emphasis on melodic instrumentals and expressive, larger-than-life vocals. This approach is rooted partly in the early influence of record producer Steve Lillywhite at a time when the band was not known for musical proficiency. The Edge has consistently used a rhythmic echo and a signature delay to craft his guitar work, coupled with an Irish-influenced drone played against his syncopated melodies that ultimately yields a well-defined ambient, chiming sound. Bono has nurtured his falsetto operatic voice and has exhibited a notable lyrical bent towards social, political, and personal subject matter while maintaining a grandiose scale in his songwriting. In addition, The Edge has described U2 as a fundamentally live band.

Despite these broad consistencies, U2 have introduced new elements into their musical repertoire with each new album. U2's early sound was influenced by bands such as Television and Joy Division, and has been described as containing a "sense of exhilaration" that resulted from The Edge's "radiant chords" and Bono's "ardent vocals". U2's sound began with post-punk roots and minimalistic and uncomplicated instrumentals heard on Boy and October, but evolved through War to include aspects of rock anthem, funk, and dance rhythms to become more versatile and aggressive. Boy and War were labelled "muscular and assertive" by Rolling Stone, influenced in large part by Lillywhite's producing. The Unforgettable Fire, which began with the Edge playing more keyboards than guitars, as well as follow-up The Joshua Tree, had Brian Eno and Daniel Lanois at the production helm. With their influence, both albums achieved a "diverse texture". The songs from The Joshua Tree and Rattle and Hum placed more emphasis on Lanois-inspired rhythm as they mixed distinct and varied styles of gospel and blues music, which stemmed from the band's burgeoning fascination with America's culture, people and places. In the 1990s, U2 reinvented themselves as they began using synthesisers, distortion, and electronic beats derived from alternative rock, industrial music, dance, and hip-hop on Achtung Baby, Zooropa, and Pop. The 2000s had U2 returning to a stripped-down sound, with less obvious use of synthesisers and effects and a more traditional rhythm.

Social and political commentary, often embellished with Christian religious and spiritual imagery, are a major aspect of U2's lyrical content. Songs such as "Sunday Bloody Sunday", "Silver and Gold", and "Mothers of the Disappeared" were motivated by current events of the time. The former was written about the troubles in Northern Ireland, while the latter concerns the struggle of mothers whose children were kidnapped and killed under Argentina's military dictatorship that began in 1976.

Bono's personal conflicts and turmoil inspired family colour songs like "Mofo", "Tomorrow" and "Kite". An emotional yearning or pleading frequently appears as a lyrical theme, in tracks such as "Yahweh", "Peace on Earth", and "Please". Much of U2's songwriting and music is also motivated by contemplations of loss and anguish, coupled with hopefulness and resiliency, themes that are central to The Joshua Tree. Some of these lyrical ideas have been amplified by Bono and the band's personal experiences during their youth in Ireland, as well as Bono's campaigning and activism later in his life. U2 have used tours such as Zoo TV and PopMart to caricature social trends, such as media overload and consumerism, respectively.

While the band and its fans often affirm the political nature of their music, U2's lyrics and music have been criticised as apolitical because of their vagueness and "fuzzy imagery", and a lack of any specific references to actual people or characters.