Southern California supports nearly 20 million people and one of the world's most prosperous economies - in a near-desert climate. Only the presence of local groundwater supplies underlying the desert makes this possible. If ever a natural resource demanded careful, controlled development, southern California groundwater does. Conventional environmental arguments contend that without centralized control, such resources are doomed. But as Dividing the Waters reveals, efficient and controlled use of southern California groundwater has emerged without either a statewide or regional government program or a "water czar." Instead, local water users have crafted self-governing institutional structures, basin by basin, watershed by watershed. These self-governing arrangements have been remarkably successful. Not only are these water supplies not depleted, they are in fact relatively healthy despite California's recent six-year drought. William Blomquist chronicles the evolution of this remarkable resource governance system in its historical and legal context, focusing on eight major southern California basins. These case studies offer many lessons about the processes by which institutional arrangements are developed, how they function, and why they work. Dividing the Waters argues strongly for replacing resource "management" with resource governance, and for enabling local users to govern effectively the resources on which they depend.