In this trenchant work, James Barrett traces the political journey of a leading worker radical whose life and experiences encapsulate radicalism's rise and fall in the United States. A self-educated wage earner raised in the slums of a large industrial city, William Z. Foster became a brilliant union organizer who helped build the American Federation of Labor and, later, radical Trade Union Educational League. Embracing socialism, syndicalism, and communism in turn, Foster rose through the ranks of the American Communist Party to stand at the forefront of labor politics throughout the 1920s. Yet by the time he died in 1961, in a Moscow hospital far from the meat-packing plants and steel mills where he had built his reputation, Foster's political marginalism stood as a symbol for the isolation of American labor radicalism in the postwar era. Integrating both the indigenous and the international factors that determined the fate of American communism, William Z. Foster and the Tragedy of American Radicalism provides a new understanding of the basis for radicalism among twentieth-century American workers.