At the heart of bluegrass music is the close ensemble playing of the major strings: mandolin, violin, banjo, and guitar, typically backed by a double bass. Alison Krauss and Union Station add one final factor that places them in the top ranks of bluegrass, and that is the strikingly pure and expressive voice of Krauss herself. Alison Krauss has been much in demand. She is a member of the Grand Ole Opry, sings with other artists, and is acclaimed for her work in the picture "O Brother, Where Art Thou?" (We should note that Dan Tyminski, another member of Union Station also contributed vocals to the film.)