This chapter outlines distinctions between national and nationalist uses of folk music as a frame for discussing its slipperiness as a concept and the political and identitarian implications of its performance, its collection and publication, its use in education and in religion, and its adoption into works of art music. Consideration of folk practices in Britain, France, Spain, and the USA from the eighteenth to the twentieth centuries is combined with special attention to expressions of Celtic otherness within nation states. The chapter also addresses the manner in which sub-national musical nationalisms (or ethnic nationalisms), operate as positive symbols of subaltern resistance and celebration when folk or folk-like material is imported into the art music of late nineteenth-century concert halls. At the same time, the chapter addresses the ‘primitivism’ of folk music and the connections nineteenth-century thinkers made between national folk musics and the precepts of social Darwinism.