While maintaining a consistent focus on health equity, social medicine has evolved with changing conditions in the region. Carter shows how it shaped early Latin American welfare states, declined with the dominance of midcentury technocratic health planning, resurged in the 1970s in solidarity against authoritarian regimes, and later resisted neoliberal reforms of the health sector. He centers socialist and anarchist doctors, political exiles, intellectuals, populist leaders, and rebellious technocrats from Argentina, Chile, Brazil, and other countries who responded to and shaped a dynamic political environment around health equity. The lessons from this history will inform new thinking about how to achieve health equity in the twenty-first century.