Theo de Jong is an allround bass guitar player living in both The Netherlands and Belgium. His instruments are the solid-body fretted and fretless bass guitar, as well as the acoustic bass guitar. He accompanies or has accompanied a lot of well-known national and international artists like Toots Thielemans, Trijntje Oosterhuis, Batida, Ekseption, Ilse DeLange, Gino Vannelli, Kaz Lux, Maurane, Philip Catherine, Dado Moroni, Dee Dee Bridgewater. Momentarily he is involved in 3HandsClapping, Peter Hertmans Quartet, Anne Wolf Trio, and Karel Boehlee Trio.

Since 1985 he teaches bass guitar and ensembles at the conservatories of Amsterdam and Utrecht. He regularly travels around in Europe to give workshops and masterclasses on several topics. Every year he teaches one week at the summer jazz camp ‘Jazz au Vert’ in Wépion, Belgium (Les lundis d’Hortence).