This paper addresses some of the confusion that has come up on what regulation means in the context of water supply and sanitation (WSS) services. In particular, it strives to answer questions about the application of the “independent regulator” model to WSS in the developing world. What types of problems can it can address effectively? What is its relevance, especially as provision and oversight of these services are often the responsibility of sub-national governments with limited resources? The Explanatory Notes on Key Topics in the Regulation of Water and Sanitation Services provide a consistent set of principles and practices that respond to these questions. Such information will be of interest to service providers, policy makers, and development practitioners interested in improving the performance of WSS services in urban areas.