Abstract: This essay presents a view of the frontiers of research on public service delivery in the developing world, based on a series of interviews with researchers and practitioners actively working in this field. It recognizes the lasting contribution of the theoretical framework laid down by the World Development Report 2004 that emphasized accountability, and the randomized evaluations that have taken place to test and develop this theory. Research on other questions, such as those relating to the analysis of politics and the structure and organization of government, is at an earlier stage, and is likely to need a more structural approach. There are many questions still to be answered in this field.