Editors' Summary: On February 7, 1983, the California Supreme Court issued an eagerly awaited decision on the application of the public trust doctrine to the appropriation of the waters feeding Northern California's Mono Lake by the City of Los Angeles. In a significant victory for environmentalists who seek to stop what they see as the draining of the unique ecological resource to slake the excessive thirst of the Southern California megalopolis, the court held that under California law the public trust must be taken into account in such appropriation decisions. Moreover, the court ruled that the state has a duty to monitor past appropriations, such as those affecting Mono Lake, and to readjust them if necessary to give effect to the public trust. In a secondary ruling the court also held that the state courts have jurisdiction concurrent with that of the state water board to resolve challenges to appropriations. Mr. Rossmann describes the background of this important case, reviews the court's holding, and considers its implications for water use and natural resource protection in California.