The public trust doctrine (PTD), an ancient anti-monopoly precept of property law inherited from Roman and civil law, exists in every United States jurisdiction and several international ones. The PTD, originally concerned with navigation and fishing, has emerged as an organizing principle for natural resources management in the twenty-first century, for it posits government trustees as stewards for both present and future generations. This casebook examines the role of the public trust doctrine in managing waterways, wetlands, water rights, wildlife, the atmosphere, and uplands like beaches and parks. The materials are suited for either an upper-division environmental or natural resources law course or a seminar.The second edition includes important new cases, including the Pennsylvania Supreme Court's landmark Robinson Township decision, the Wisconsin Supreme Court's narrowing of the public trust doctrine in Rock Koshkonong, and several recent cases in the atmospheric trust litigation.