MUSICAL GROUPS SUCH AS the Lilly Brothers obviously have many external and internal forces acting on them that account for the music they play at any particular moment. Choice of material and style are the result of the meshing of these forces. Personal relationships, aspirations, cultural context, physical conditions, and economic conditions all contribute, and none can be meaningfully studied in isolation without a general understanding of the other major forces that are operant; thus, the issues and events broached here are only the grossest set of events that can be said to influence the musical evolution of the Lilly Brothers, who are a traditional southern Appalachian band that was professionally active between 1938-I970 and that still plays occasional dates. The Lilly Brothers are an important traditional hillbilly band from many points of view, but this article is primarily concerned with their relationship to bluegrass music, the only remaining commercially viable type of traditional stringband music. I will first look at the general evolution of this music in the time period 1920-x97o and then look at the Lilly Brothers' professional career in an effort to tie the general context of old-timey bluegrass music to the specific context of their music.