For students of American and western water law, the Colorado River presents an unmatched union of hydrology, history, demography, and jurisprudence. This class will explore the River’s influence on state, national, and international law. Drawing on both historical and legal sources, we will first address the unprecedented efforts of the seven basin states to allocate the River voluntarily. We will focus on Congressional efforts to balance California’s immediate desire to harness the river, with protection of the upstream states and their future development; and the seminal interpretation of that effort in the Supreme Court’s momentous water law ruling, Arizona v. California. Before turning to the states’ responses to that 1963 decision, we examine its extraordinary impact within California, igniting classic battles at the Owens Valley, Mono Lake, Sacramento Delta, and Salton Sea. We then examine contemporary efforts to deal with shortage, both anthropogenic (overdevelopment) and natural (climate change), and international efforts to attain equity with Mexico. We conclude by attempting to essay the River’s influence on the future of the American Southwest and the entire Nation.