This week PLoS Medicine publishes the last in a four-part series of policy papers examining the ways in which global health institutions and arrangements are changing and evolving.

In this fourth paper, Suerie Moon (John F. Kennedy School of Government, Harvard University, USA) and colleagues argue that an effective global health system must accomplish at least five core functions: agenda-setting; financing and resource allocation; research and development; implementation and delivery; and monitoring, evaluation, and learning. They discuss ways to improve each of these five functional areas, consider the implications for the role of the World Health Organization (WHO), and make recommendations for future action.