This article analyzes Brazil's Unified Health System (SUS), established by the 1988 Constitution. The article initially presents the previous trajectory of national health policy and the context of democratization in the 1980s, which favored health reform and created a public, universal, and comprehensive health system. It then explores the advances and contradictions recorded in more than three decades of implementation of the SUS. The main advances observed were the creation of institutional mechanisms compatible with the federative arrangement and social participation, political and administrative decentralization, the national expansion of access to health, changes in the health care model, including strengthening primary care, and improvements in health indicators. On the other hand, the persistence of structural problems and disputes between different health agendas, with differences between governments, led to contradictions in financing and public-private relations in health. Despite the differences between countries, the analysis of the Brazilian case provides lessons on the challenges in building universal health systems in Latin America.