Crosby, Stills & Nash have remained America's longest-running experiment in vocal harmony and social relevance. The trio brought harmony to the forefront of popular music with their unique three-part vocal blend. A low-key supergroup, they emphasized singing and songwriting above all, and their example contributed to the evolution of the singer/songwriter movement in the Seventies. Born out of well-known groups that placed a premium on harmony, Crosby, Stills & Nash boasted impressive individual credentials before they joined forces in 1969. David Crosby sang and played rhythm guitar with the Byrds. Stephen Stills was a mainstay of Buffalo Springfield. Nash provided the high harmonies that helped make pop sensations of Britain's Hollies. Even with those estimable prior alliances, Crosby, Stills & Nash would become their pinnacle as musicians.