Crosby, Stills & Nash (CSN) was a folk rock supergroup composed of the American singer-songwriters David Crosby and Stephen Stills and the English-American singer-songwriter Graham Nash. When joined by the Canadian singer-songwriter Neil Young, they were known as Crosby, Stills, Nash & Young (CSNY). They are noted for their intricate vocal harmonies and lasting influence on American music and culture, their political activism and their tumultuous relationships.