Peter Lawrence Buck (born December 6, 1956) is an American musician and songwriter. He was a co-founder and the lead guitarist of the alternative rock band R.E.M. He also plays the banjo and mandolin on several R.E.M. songs. Throughout his career with R.E.M. (1980–2011), as well as during his subsequent solo career, Buck has also been at various times an official member of numerous 'side project' groups. These groups included Arthur Buck (with Joseph Arthur), Hindu Love Gods, The Minus 5, Tuatara, The Baseball Project, Robyn Hitchcock and the Venus 3, Tired Pony, The No-Ones and Filthy Friends, each of which have released at least one full-length studio album. Additionally, the experimental combo Slow Music (which also features Fred Chalenor, Hector Zazou, Matt Chamberlain, Robert Fripp, and Bill Rieflin) have released an official live concert CD. Another side project group called Full Time Men released an EP while Buck was a member. As well, ad hoc "supergroups" Bingo Hand Job (Billy Bragg and R.E.M.), Musical Kings (Michelle Malone, Peter Buck, John Keane) and Nigel & The Crosses (Robyn Hitchcock, Peter Buck, Glenn Tilbrook and others) have each commercially released one track.

"Richard M. Nixon", a band Buck founded in 2012 to support the release of his solo album with live gigs, has never issued an official recording. Richard M. Nixon consists of Buck, Scott McCaughey and Bill Rieflin, the same three musicians who comprise The Venus 3.

Buck also has a career as a record producer including releases by Uncle Tupelo, Vigilantes of Love, Dreams So Real, The Fleshtones, The Feelies, and The Jayhawks, as well as a session musician (for the likes of The Replacements, Billy Bragg, Decemberists and Eels).