A girl group is a popular music act featuring several female singers who generally harmonize together. Girl groups have been popular at least since the heyday of the Boswell Sisters beginning in the 1930s, but the term "girl group" also denotes the wave of American female pop singing groups who flourished in the late 1950s and early 1960s between the decline of early rock and roll and the British Invasion, many of whom were influenced by doo-wop style. This article covers only girl groups from that era and later.