luegrass is a style of country music based on the sound of Bill Monroe and his band, the Blue Grass Boys. It is characterized by fast tempos, keening vocals, virtuosic delivery, and the fusion of several styles of traditional American folk music, including string bands, fiddle music, and gospel harmonies. The music is nearly always performed on some combination of the following acoustic instruments: guitar, mandolin, fiddle, banjo, string bass, and dobro. Photo of John Hartford by David Schenk.