A sideman is a professional musician who is hired to perform or record with a group of which he or she is not a regular member. They often tour with solo acts as well as bands and jazz ensembles. Sidemen are generally required to be adaptable to many different styles of music, and so able to fit smoothly into the group in which they are currently playing. Often aspiring musicians start out as sidemen, and then move on to develop their own sound, a name, and fans of their own, or go on to form their own groups. Some examples of this are:

• James Burton and Glen D. Hardin, playing guitar and keyboards respectively, who performed in the backing band for Elvis Presley, also backed Gram Parsons before joining newcomer Rodney Crowell and veteran Albert Lee in Emmylou Harris' "Hot Band".
• Don Henley and Glenn Frey were in the initial backup band for Linda Ronstadt, which toured in support of her eponymous debut album. Afterwards, with the addition of Joe Walsh and Don Felder, (and later, Timothy Schmit), they formed the Eagles.