The revolutionary appeal of Communism in 20th-century Britain is analyzed in this examination of why Communist Party members joined, how they participated in the party's activities, and why, in many cases, they left the party. Archival resources, hundreds of interviews, and sociological analyses document the nature of left-wing activism in Britain from its earliest incarnations to the schisms of the 1980s. The role of Communism in British politics and society is illuminated by discussions of constructions of political authority; the role of gender, generation, and social class; and the significance of political space and mobility in recruitment.