The Firesign Theatre (also known as the Firesigns) was an American surreal comedy troupe who first appeared on November 17, 1966, in a live performance on the Los Angeles radio program Radio Free Oz on station KPFK FM. They continued appearing on Radio Free Oz, which later moved to KRLA 1110 AM and then KMET FM, through February 1969. They produced fifteen record albums and a 45 rpm single under contract to Columbia Records from 1967 through 1976, and had three nationally syndicated radio programs: The Firesign Theatre Radio Hour Hour [sic] in 1970 on KPPC-FM; and Dear Friends (1970–1971) and Let's Eat! (1971–1972) on KPFK. They also appeared in front of live audiences, and continued to write, perform, and record on other labels, occasionally taking sabbaticals during which they wrote or performed solo or in smaller groups.

The Firesign Theatre was the brainchild of Peter Bergman, and all of its material was conceived, written, and performed by its members: Bergman, Philip Proctor, Phil Austin, and David Ossman. The group's name stems from astrology, because all four were born under the three "fire signs": Aries (Austin), Leo (Proctor), and Sagittarius (Bergman and Ossman). Their popularity peaked in the early 1970s and ebbed in the Reagan era. They experienced a revival and second wave of popularity in the 1990s and continued to write, record and perform until Bergman's death in 2012.

In 1997, Entertainment Weekly ranked the Firesign Theatre among the "Thirty Greatest Comedy Acts of All Time". Their 1970 album Don't Crush That Dwarf, Hand Me the Pliers was nominated in 1971 for the Hugo Award for Best Dramatic Presentation by the World Science Fiction Society, and their next album I Think We're All Bozos on This Bus received the same nomination in 1972. Later, they received nominations for the Grammy Award for Best Comedy Album for three of their albums: The Three Faces of Al (1984), Give Me Immortality or Give Me Death (1998), and Bride of Firesign (2001). In 2005, the US Library of Congress added Don't Crush That Dwarf to the National Recording Registry and called the group "the Beatles of comedy."