A girl group is a popular music act featuring several young female singers who generally harmonise together.

Girl groups emerged in the late 1950s as groups of young singers teamed up with behind-the-scenes songwriters and music producers to create hit singles, often featuring glossy production values and backing by top studio musicians. In later eras the girl group template would be applied to disco, contemporary R&B, and country-based formats as well as pop.

A distinction is made here with all-female bands, in which members also play instruments, though this terminology is not universally followed.

During the Music Hall/Vaudeville era, all-girl singing groups were mainly novelty acts singing nonsense songs in silly voices. One of the first major exceptions was the Hamilton Sisters and Fordyce, an American trio who succesfully toured England and parts of Europe in 1927, recorded and appeared on BBC radio - they toured the US variety and Big-time Theaters extensively later changed their stage name to the Three X Sisters (the ladies were together singing from 1923 until the early 1940s) known for close harmonizing, as well as, barbershop style or novelty tunes, and utilized their 1930s radio success. Boswell Sisters, who became one of the most popular singing groups from 1930 to 1936, with over twenty hits. The Andrews Sisters started (1937) as a Boswell tribute band and continued recording and performing through the 1940s into the late-1960s, achieving more record sales, more Billboard hits, more million-sellers, and more movie appearances than any other girl group to date.