Sgt. Pepper's Lonely Hearts Club Band (often shortened as Sgt. Pepper) is the eighth studio album by the English rock band The Beatles, released on 1 June 1967 on the Parlophone label and produced by George Martin. The album is widely regarded as one of the greatest of all time, and has since been recognised as one of the most important albums in the history of popular music, including songs such as "Lucy in the Sky with Diamonds" and "A Day in the Life".

Recorded over a 129-day period beginning in December 1966, Sgt. Pepper saw the band developing the production techniques of their previous album, Revolver. Martin's innovative and lavish production included the orchestra usage and hired musicians ordered by the band. Genres such as music hall, jazz, rock and roll, western classical, and traditional Indian music are covered. The album cover art, by English pop artist Peter Blake, depicts the band posing in front of a collage of their favourite celebrities, and has been widely acclaimed and imitated.

Sgt. Pepper was a worldwide critical and commercial success, spending a total of 27 weeks at the top of the UK Album Chart and 15 weeks at number one on the US Billboard 200. A defining album in the emerging psychedelic rock style, the album was critically acclaimed upon release and won four Grammy awards in 1968. It frequently ranks at or near the top of published lists of the greatest albums of all time. In 1994 it was ranked number one in the book All Time Top 1000 Albums. In 2003, the album was placed at number one on Rolling Stone magazine's list of the "500 Greatest Albums of All Time". Sgt. Pepper is one of the world's best selling albums, having shipped 32 million copies.