U2 are an Irish rock band formed in Dublin in 1976. The group comprises Bono (lead vocals and rhythm guitar), the Edge (lead guitar, keyboards, and backing vocals), Adam Clayton (bass guitar), and Larry Mullen Jr. (drums and percussion). Initially rooted in post-punk, U2's musical style has evolved throughout their career, yet has maintained an anthemic quality built on Bono's expressive vocals and the Edge's chiming, effects-based guitar sounds. Bono's lyrics, often embellished with spiritual imagery, focus on personal and sociopolitical themes. Popular for their live performances, the group have staged several elaborate tours over their career.

The band was formed when the members were teenaged pupils of Mount Temple Comprehensive School and had limited musical proficiency. Within four years, they signed with Island Records and released their debut album, Boy (1980). Works such as their first UK number-one album, War (1983), and singles "Sunday Bloody Sunday" and "Pride (In the Name of Love)" helped establish U2's reputation as a politically and socially conscious group. Their fourth album, The Unforgettable Fire (1984), was their first collaboration with producers Brian Eno and Daniel Lanois, whose influence resulted in a more abstract, ambient sound for the band. By the mid-1980s, U2 had become renowned globally for their live act, highlighted by their performance at Live Aid in 1985. Their fifth album, The Joshua Tree (1987), made them international stars and was their greatest critical and commercial success. One of the world's best-selling albums with 25 million copies sold, it produced the group's only number-one singles in the US to date: "With or Without You" and "I Still Haven't Found What I'm Looking For".

Facing creative stagnation and a backlash to their documentary and double album Rattle and Hum (1988), U2 reinvented themselves in the 1990s. Beginning with their acclaimed seventh album, Achtung Baby (1991), and the multimedia spectacle of the Zoo TV Tour, the band pursued a new musical direction influenced by alternative rock, electronic dance music, and industrial music, and they embraced a more ironic, flippant image. This experimentation continued on Zooropa (1993) and concluded with Pop (1997) and the PopMart Tour. All That You Can't Leave Behind (2000) and How to Dismantle an Atomic Bomb (2004), saw a return to a more conventional, mainstream sound. The U2 360° Tour of 2009–2011 set records for the highest-attended and highest-grossing concert tour, which stood until 2019. Songs of Innocence (2014) received criticism for its pushed release through the iTunes Store. In 2023, U2 released Songs of Surrender, an album of re-recorded songs, and began the U2:UV Achtung Baby Live concert residency to inaugurate Sphere in the Las Vegas Valley.

U2 have released 15 studio albums and are one of the world's best-selling music artists, having sold an estimated 150–170 million records worldwide. They have won 22 Grammy Awards—the most of any band—and in 2005, they were inducted into the Rock and Roll Hall of Fame in their first year of eligibility. According to Pollstar, they were the second-highest-grossing live music artist from 1980 to 2022, earning US$2.13 billion. Rolling Stone ranked U2 at number 22 on 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 social justice causes, working with organisations and coalitions that include Amnesty International, Jubilee 2000, DATA/the ONE Campaign, Product Red, War Child, and Music Rising.