John Sidney Linnell is an American musician and one half of the Brooklyn-based alternative rock band They Might Be Giants with John Flansburgh, which was formed in 1982. In addition to singing and songwriting, he plays accordion, baritone and bass saxophone, clarinet, and keyboards for the group.

They Might Be Giants, often abbreviated as TMBG, is an American alternative rock band formed in 1982 by John Flansburgh and John Linnell. During TMBG's early years, Flansburgh and Linnell frequently performed as a musical duo, often accompanied by a drum machine. In the early 1990s, TMBG expanded to include a backing band. The duo's current backing band consists of Marty Beller, Dan Miller and Danny Weinkauf. They have been credited as vital in the creation and growth of the prolific DIY music scene in Brooklyn in the mid-1980s.