Session musicians, also called studio musicians, are instrumental and vocal performers who are available to work with others at live performances or recording sessions. Usually such musicians are not permanent members of a musical ensemble with the singers that they are accompanying and they often do not achieve individual fame in their own right as soloists or bandleaders. However, some backing bands of session musicians have become well known (e.g., The Wrecking Crew).

The term is applied to those working in all musical styles. Versatility is one of the most important skills of session musicians as they may have to perform in a range of different settings. Session musicians are expected to learn parts rapidly and be skilled in both sight reading and improvising chords or a bassline from a lead sheet or chord chart (or, in country music, a song chart in the Nashville number system).

Session musicians are used in any situation where musical skills are needed on a short-term basis. Typically session musicians are used by recording studios to provide backing tracks for other musicians for recording sessions and live performances; recording for advertising, film and television; or theatrical productions. Some session musicians formed a rhythm section that was repeatedly used for recordings.