The Who are an English rock band formed in London in 1964. Their classic lineup (1964–1978) consisted of lead vocalist Roger Daltrey, guitarist Pete Townshend, bassist John Entwistle and drummer Keith Moon. They are considered one of the most influential rock bands of the 20th century. Their contributions to rock music include the development of the Marshall stack, large public address systems, the use of synthesisers, Entwistle's and Moon's influential playing styles, Townshend's feedback and power chord guitar technique, and the development of the rock opera. They are cited as an influence by many hard rock, punk, power pop and mod bands. The Who were inducted into the Rock and Roll Hall of Fame in 1990.

The Who evolved from an earlier group, the Detours, and established themselves as part of the pop art and mod movements, featuring auto-destructive art by destroying guitars and drums on stage. Their first single as the Who, "I Can't Explain" (1965), reached the UK top ten, and was followed by a string of hit singles including "My Generation" (1965), "Substitute" (1966) and "Happy Jack" (1966). In 1967, they performed at the Monterey Pop Festival and released "I Can See for Miles", their only US top-ten single. The group's 1969 concept album Tommy included the single "Pinball Wizard" and was a critical and commercial success.

Further festival appearances at Woodstock and the Isle of Wight, along with the concert album Live at Leeds (1970), established their reputation as a respected rock act. The success put pressure on lead songwriter Townshend, and the follow-up to Tommy, Lifehouse, was abandoned. Songs from the project made up the album Who's Next (1971), including the hits "Won't Get Fooled Again", "Baba O'Riley", and "Behind Blue Eyes". The group released another concept album, Quadrophenia (1973), as a celebration of their mod roots, and oversaw the film adaptation of Tommy (1975). They continued to tour to large audiences before semi-retiring from live performances at the end of 1976. The release of Who Are You (1978) was overshadowed by Moon's death shortly after.

Kenney Jones replaced Moon and the group resumed touring, and released a film adaptation of Quadrophenia and the retrospective documentary The Kids Are Alright. After Townshend became weary of the group, they split in 1983. The Who occasionally re-formed for live appearances such as Live Aid in 1985, a 25th-anniversary tour in 1989 and a tour of Quadrophenia in 1996–1997. A full reunion began in 1999, with drummer Zak Starkey. After Entwistle's death in 2002, plans for a new album were delayed until 2006, with Endless Wire. Since Entwistle's death, The Who have continued to perform and tour, most commonly with Starkey on drums, Pino Palladino on bass, and Pete's brother Simon Townshend on second guitar and backing vocals. In 2019, the group released the album Who and toured with a symphony orchestra.