Bluegrass forms part of the great American roots tradition and is related to country and folk. The genre grew out of mountain music or hillbilly music in the Appalachians in south east USA. The name comes from Kentucky, where "the grass is so green that it's blue." Mandolin virtuoso Bill Monroe is often called the Father of Bluegrass, due to his success in the 1940s with his band, the Blue Grass Boys. One of the band was another trend-setter, Earl Scruggs on five-string banjo.
Bluegrass has also roots in Irish, Scots and English folk music and is related to old-time, blues and jazz. The music is driven by a solid back-beat and is often played in a fast tempo. As in jazz, there is space for instrumental improvisation. A standard bluegrass band has three to five members, and the typical instruments are mandolin, banjo, guitar, violin and double bass. Singing is central to bluegrass and is often characterised by close harmonies and a high register.