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Session musicians, studio musicians, or backing musicians are musicians hired to perform in recording sessions or live performances. Session musicians are usually not permanent members of a musical ensemble or band. They work behind the scenes and rarely achieve individual fame in their own right as soloists or bandleaders. However, top session musicians are well-known within the music industry, and some have become publicly recognized, such as the Wrecking Crew and Motown's The Funk Brothers.

Many session musicians specialize in playing common instruments such as guitar, piano, bass, or drums. Others are specialists, and play brass, woodwinds, and strings. Many session musicians play multiple instruments, which lets them play in a wider range of musical situations, genres and styles. Examples of "doubling" include double bass and electric bass; acoustic guitar and mandolin; piano and accordion; and saxophone and other woodwind instruments.

Session musicians are used when 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 music for advertising, film, television, and theatre. In the 2000s, the terms "session musician" and "studio musician" are synonymous, though in past decades, "studio musician" meant a musician associated with a single record company, recording studio or entertainment agency.

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