Originally Posted by Wikipedia

Bluegrass music is a form of American roots music, and is a sub-genre of country music. It has roots in Scottish, English, Welsh and Irish traditional music. Bluegrass was inspired by the music of immigrants from the United Kingdom and Ireland (particularly the Scotch-Irish immigrants in Appalachia). In bluegrass, as in some forms of jazz, one or more instruments each takes its turn playing the melody and improvising around it, while the others perform accompaniment; this is especially typified in tunes called breakdowns. This is in contrast to old-time music, in which all instruments play the melody together or one instrument carries the lead throughout while the others provide accompaniment. Traditional bluegrass is typically based on a small set of acoustic stringed instruments including mandolin, acoustic guitar, banjo, fiddle, resonator guitar and upright bass, with or without vocals.
Bluegrass music has attracted a diverse and loyal following worldwide. Bluegrass pioneer Bill Monroe characterized the genre: "Scottish bagpipes and ole-time fiddlin'. It's Methodist and Holiness and Baptist. It's blues and jazz, and it has a high lonesome sound. It's plain music that tells a good story. It's played from my heart to your heart, and it will touch you. Bluegrass is music that matters."