For what it is worth, modern bluegrass didn't really come to vogue as Mark rightly points out. However, (and there are a lot of howevers in history and in musical history) Bluegrass is a dirivative of Appalachian hill music which was direct offspring of folk music brought over from the British Isles most notably Scotland and Ireland. But English and Welsh music were instrumental also. As I understand it, Blues derives from African roots and grew in popularity in the bordellos of New Orleans, spreading throughout the US as musicians travelled around looking for work. There are common themes and bluesmen did jam with bluegrass musicians. Hope this helps and is accurate, Neil