Session 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 and often do not achieve fame in their own right as soloists or bandleaders. The term is applied not only to those working in contemporary musical styles such as rock, jazz, country, R&B and pop but also classical music. 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 ear training.

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 in recording studios and live performances; recording for advertising, film and television; or theatrical productions.