Kleissonic is a boutique guitar pedal builder founded in 2009 by electronic engineer Theodor Kleissiaris (Theo Kleissiaris). The company started in Berlin, Germany, where Kleissiaris built the brand around hand-assembled, original circuit designs aimed at experimental and noise-leaning guitarists. In 2019, operations relocated to Greece, where Kleissiaris continues to design circuits, create artwork, and assemble each pedal in-house.

The brand's catalog focuses on fuzz, modulation, and delay effects with a leftfield, textural slant rather than vintage reissues or clones. Notable models include the Screaming Skull, a self-oscillating fuzz that became Kleissonic's bestseller; the Lucid, a minimal two-knob fuzz with Volume and Harmonics controls; the Howl, a two-notch phase shifter with Volume, Gain, and Sweep controls and no internal LFO; and the Echolapse, an analog-voiced delay that emulates a tape echo with a 42ms–900ms time range. Pedals are housed in cast-aluminum enclosures finished in-house, from drilling through artwork.

Kleissonic has built a following among experimental and post-rock musicians. Players associated with the brand include Lee Ranaldo of Sonic Youth, John Cummings of Mogwai, and Efrim Menuck and David Bryant of Godspeed You! Black Emperor, with the brand also citing work for artists from Wooden Shjips, The Brian Jonestown Massacre, and The Black Angels.

Kleissonic has 2 products cataloged on Equipboard, including Fuzz Effects Pedals and Tremolo Effects Pedals.