Guster is an American alternative rock band from Boston, Massachusetts, United States. Founding members Adam Gardner, Ryan Miller, and Brian Rosenworcel began practice sessions while attending Tufts University in Medford, Massachusetts, and formed the band in 1991. The members met during the freshman Wilderness Orientation program in August of that year, playing publicly together as a trio two months later at the Midnight Cafe coffee house set in the common area of the Lewis Hall dormitory. While attending Tufts, the band lived at 139 College Avenue in Somerville, Massachusetts.

The band stayed "underground" for its first two full-length albums, Parachute (1994) and Goldfly (1997), but broke into the musical mainstream in 1999 with its third studio album Lost and Gone Forever, featuring the single "Fa Fa", which made it onto the Adult Top 40. The band enjoyed moderate success on the charts with Keep It Together, its fourth album, with two singles in the Adult Top 40 ("Careful" and "Amsterdam"). Joe Pisapia joined the official lineup for Keep It Together and its follow-up, Ganging Up on the Sun, which peaked at 25 on the Billboard 200. A variety of television shows and movies have featured the band's music, including Martian Child, which featured their song "Satellite"; Disturbia; Wedding Crashers; Life as a House, which makes several allusions to the band throughout the film; The O.C.; and one of the band's songs was used in an ad for The Weather Channel. The band earned its first gold record in 2018 for its single "Satellite".

Guster's tours were originally local, but began to spread as the band gained popularity. In 1999, Guster gave its first performance in Canada, followed by a 2004 tour in Britain that had four shows in London and one in Manchester. Guster maintains a liberal taping policy and has a very dedicated and active taping community. In addition, the band has released several live shows via iTunes.