Brazil's Sistema Unico de Saude (SUS), a universal, publicly-funded, rights-based health system, designed and put in place in an era where neo-liberal reforms elsewhere in the world have driven the marketization of health services, offers important lessons for future health systems. In this article, we focus on the innovative institutional mechanisms for popular involvement and accountability that are part of the architecture for governance of the SUS. We argue that these mechanisms of public involvement hold the potential to sustain a compact between state and citizens and ensure the political momentum required to broaden access to basic health services, while at the same time providing a framework for the emergence of "regulatory partnerships" capable of managing the complex reality of pluralistic provision and multiplying sources of health expertise in a way which ensures that the needs and rights of poor and marginalised citizens are not relegated to the periphery of a segmented health system.