The Firesign Theatre is a comedy troupe consisting of Phil Austin, Peter Bergman, David Ossman, and Philip Proctor. 

The troupe began as live radio performers in Los Angeles, California on radio stations KPPC and KPFK during the late 1960s and early 1970s. Firesign Theatre specializes in audio recordings, with relatively little presence in stage performance, television or movies. Their first four albums in particular are considered classics of recorded comedy.

The Firesign Theatre authored two books; The Firesign Theatre's Big Book Of Plays and The Firesign Theatre's Big Mystery Joke Book.

During the mid-1970s, the group more or less split in half: Firesign productions continued, but Proctor and Bergman also performed as a duo, and Austin and Ossman worked individually and together in a few stage shows.