[Forum: twenty years of experience and the challenge with the Unified National Health System. Introduction].

This Introduction presents the Forum on the 20 years of experience with the Unified National Health System (SUS), consisting of 3 articles and a postscript. The first article provides a historical overview of the implementation of the SUS, in light of the Constitutional provisions pertaining to health. It discusses the context and main issues underlying the creation of the SUS in Brazil and proposes a renewed linkage between health sector policies and an expanded project for Brazilian society. The second article analyzes the SUS' dynamics; strides in access to and comprehensiveness of care; and challenges for the achievement of its objectives, in light of factors that are external to the system, involving the need for greater politicization of analyses on the issue. The third article approaches social and political processes that developed from 1988 to 2008. It mainly analyzes the history of two collegiate bodies under the SUS at the Federal level: the National Health Council and the Tripartite Inter-Managers' Commission. Despite the complexity identified by the authors and the important obstacles they identify, the reflections indicate that the SUS has been a successful social policy, besides contributing to the consolidation of democracy in Brazil.