Bassline (also known as a bass line or bass part) is the term used in many styles of music, such as blues, jazz, funk, dub and electronic, traditional, or classical music for the low-pitched instrumental part or line played (in jazz and some forms of popular music) by a rhythm section instrument such as the electric bass, double bass, cello, tuba or keyboard (piano, Hammond organ, electric organ, or synthesizer).

In unaccompanied solo performance, basslines may simply be played in the lower register of any instrument while melody and/or further accompaniment is provided in the middle or upper register. In solo music for piano and pipe organ, these instruments have an excellent lower register that can be used to play a deep bassline. On organs, the bass line is typically played using the pedal keyboard and massive 16' and 32' bass pipes.