This book explores the political trajectory of Latin America's most important contemporary labor movement. The New Unionism played a central role in Brazil's struggle for democracy in the 1980s and recast the country's subsequent party politics through its creation of the innovative Workers' Party (PT). The author breaks new ground by analyzing this celebrated prototype of social movement unionism as a heterogeneous alliance of component factions that evolves in relation to shifting economic, political, and ideological contexts. Through the prism of internal politics, he shows how Brazil's transitions - from military-authoritarian to liberal-democratic rule, from statist to free-market economic policies, and from a Leninist to a post-Leninist left - undermined the independent labor movement's commitments to internal democracy, political autonomy, and societal transformation. The book concludes with a comparative assessment of Brazilian, South African, and South Korean social movement unionisms' shared dilemmas, arguing that an adequate understanding of their relative declines demands more rigorous attention to the dynamic nexus between internal movement politics and shifting external environments.