Esa Onttonen (b. 1975) is a composer and guitarist living in Helsinki, Finland. He mainly works in the field of jazz and improvised music but he has also played rock riffs on electric guitar and written scores for classical ensembles. He is a co-leader of groups Gourmet and Gnomus which have released a total of seven albums and performed in Belgium, Estonia, Czech Republic, France, Germany, the Netherlands and Russia, in addition to several tours in Finland. His regular collaborators include saxophonist Mikko Innanen, drummer Mika Kallio and pianist Kari Ikonen. Along with Onttonen they are also the founders of the record label Fiasko Records.

Onttonen has written commissioned compositions and arrangements for orchestras such as Finnish Radio Symphony Orchestra, UMO Jazz Orchestra, Virtuosi di Kuhmo, St. Michel Strings (Mikkelin kaupunginorkesteri), Uusinta Chamber Ensemble, Kaartin Seitsikko, Jyväskylä Big Band and Avanti! (with Badu Ndjai), and soloists Jukka Gustavson, Mikko Innanen, Anna-Mari Kähärä, Jukka Perko, Tomasz Stanko. He has worked in artist residencies in Paris, Rome and Prague.

As guitarist Onttonen has played and recorded with his own co-led groups Gnomus and Gourmet and as sideman with Hepa Halme Prospekt, Mirja Mäkelä, Jukka Orma's Revolution Soul Band, Ari Poutiainen, Jenny Robson and many others. His style ranges from traditional guitar aesthetics to free improvisation utilizing a wide spectrum of sounds available from electric guitar and various effects.

In 2000 Onttonen started teaching music theory at Jazz Music Department of Sibelius Academy where he received Master of Music degree in 2001. Later he's been teaching mainly composing and arranging on part- and full-time basis at various Finnish higher education institutions.