SynthAxe is an English musical instrument company founded by Bill Aitken, with engineers Mike Dixon and Tony Sedivy, that produced a fretted, guitar-shaped MIDI controller of the same name beginning in 1985. Developed in the late 1970s and brought to market with funding from Richard Branson's Virgin Group, the instrument was conceived not as a guitar but as a new kind of controller — one that decoupled fretting from triggering, with a separate set of strings on the body for picking and a second set on the angled neck for fretting, plus a row of trigger keys for sustain, vibrato and dynamics. The fretboard was continuously scanned and the resulting MIDI data was used to drive external synthesizers, since the SynthAxe itself has no onboard sound engine.

Fewer than 100 units were built, with launch pricing around £10,000, and production was short-lived, making surviving examples rare and collectible. Despite the limited run, the SynthAxe became one of the most recognizable guitar-synth controllers of the 1980s and a touchstone in discussions of guitar-to-MIDI design. Its most prominent advocate was Allan Holdsworth, who used it extensively on records including Atavachron, Sand and Flat Tire. Other notable users included Lee Ritenour, who featured it on Earth Run, Chuck Hammer, and percussionist Roy "Futureman" Wooten of Béla Fleck and the Flecktones.

SynthAxe has 2 products cataloged on Equipboard, including Digital Modeling Guitars and Controllers. Their gear is featured by 6 artists, with the strongest followings in Rock, Electronic, and Pop. Notable users include Gary Moore, Allan Holdsworth, and Lee Ritenour.