The Beastie Boys were an American hip-hop group formed in New York City in 1981. They were composed of Adam "Ad-Rock" Horovitz (vocals, guitar), Adam "MCA" Yauch (vocals, bass), and Michael "Mike D" Diamond (vocals, drums). The Beastie Boys were formed out of members of experimental hardcore punk band the Young Aborigines, which was formed in 1979, with Diamond on drums, Jeremy Shatan on bass guitar, John Berry on guitar, and Kate Schellenbach later joining on percussion. When Shatan left New York City in mid-1981, Yauch replaced him on bass and the resulting band was named the Beastie Boys. Berry left shortly thereafter and was replaced by Horovitz.

After achieving local success with the 1983 comedy hip hop single "Cooky Puss", the Beastie Boys made a full transition to hip hop, and Schellenbach left. They toured with Madonna in 1985 and a year later released their debut album, Licensed to Ill (1986), the first rap album to top the Billboard 200 chart. Their second album, Paul's Boutique (1989), was made with significant contributions by the Dust Brothers and composed almost entirely of samples. It was a commercial failure that later received critical acclaim. Check Your Head (1992) and Ill Communication (1994) found mainstream success, followed by Hello Nasty (1998), To the 5 Boroughs (2004), The Mix-Up (2007), and Hot Sauce Committee Part Two (2011).

The Beastie Boys have sold 20 million records in the United States and had seven platinum-selling albums from 1986 to 2004. They are the biggest-selling rap group since Billboard began recording sales in 1991. In 2012, they became the third rap group to be inducted into the Rock and Roll Hall of Fame. In the same year, Yauch died of cancer and the Beastie Boys disbanded. The remaining members have released several retrospective works, including a book, a documentary, and a career-spanning compilation album.

Prior to forming the Beastie Boys, Michael Diamond was part of a number of bands such as the Walden Jazz Band, and BAN. The Young Aborigines formed in 1979. In 1981, when Young Aborigines bassist Jeremy Shatan left New York City for the summer, the remaining members Diamond, John Berry and Kate Schellenbach began to perform as the Beastie Boys with Adam Yauch.

In a 2007 interview with Charlie Rose, Yauch recalled that it was Berry who suggested the name the Beastie Boys. Although the band stated that "Beastie" is an acronym standing for "Boys Entering Anarchistic States Towards Inner Excellence", in the Charlie Rose interview, both Yauch and Diamond acknowledged that the acronym was an "afterthought" conceived after the name was chosen. The band supported Bad Brains, the Dead Kennedys, the Misfits and Reagan Youth at venues such as CBGB, A7, Trude Heller's and Max's Kansas City, playing at the latter venue on its closing night. In November 1982, the Beastie Boys recorded the 7-inch EP Polly Wog Stew at 171A studios, an early recorded example of New York hardcore.

On November 13, 1982, the Beastie Boys played Philip Pucci's birthday for the purposes of his short concert film, Beastie. Pucci held the concert in Bard College's Preston Drama Dance Department Theatre. This performance marked the Beastie Boys' first on-screen appearance in a published motion picture. Pucci's concept for Beastie was to distribute a mixture of both a half dozen 16 mm Bell & Howell Filmo cameras, and 16 mm Bolex cameras to audience members and ask that they capture the Beastie Boys performance from the audience's own point of view while a master sync sound camera filmed from the balcony of the abandoned theater where the performance was held. The opening band for that performance was the Young and the Useless, which featured Adam Horovitz as the lead singer. A one-minute clip of Beastie was subsequently excerpted and licensed by the Beastie Boys for use in the "Egg Raid on Mojo" segment of the "Skills to Pay the Bills" long-form home video released by Capitol Records. "Skills to Pay the Bills" later went on to be certified Gold by the Recording Industry Association of America (RIAA). Berry left the group in 1982 (later forming Thwig, Big Fat Love and Bourbon Deluxe) and was replaced by Horovitz, who had become close friends with the Beastie Boys.

The band also recorded and then performed its first hip hop track, "Cooky Puss", based on a prank call by the group to a Carvel Ice Cream franchise in 1983. It was a part of the new lineup's first EP, also called Cooky Puss, which was the first piece of work that showed their incorporation of the underground rap phenomenon and the use of samples. It quickly became a hit in New York underground dance clubs and night clubs. After "Beastie Revolution" was later sampled in a British Airways commercial, the Beastie Boys threatened to sue them over the use of the song, and the airline immediately paid them $40,000 in royalties.

Following the success of "Cooky Puss", the band began to incorporate rap into their sets. They hired a DJ for their live shows, New York University student Rick Rubin, who began producing records soon thereafter. "I met Mike first," Rubin recalled. "I thought he was an arrogant asshole. Through spending time with the Beasties I grew to see that they had this great sense of humor. It wasn't that they were assholes, and even if it was, they were funny with it." Rubin formed Def Jam Recordings with Russell Simmons, and approached the band about producing them for his new label. As the band was transitioning to hip hop, Schellenbach was fired in 1984, with Diamond taking over on drums. In their 2018 memoir, Ad-Rock expressed regret for firing Schellenbach, which he attributed to her not fitting with the "new tough-rapper-guy identity".