The public trust doctrine is an ancient doctrine of public property law that governs sovereign stewardship of natural resources. The doctrine both promote public access to trust resources and requires sovereign protection of them for the benefit of the public, including future generations. The doctrine, which first surfaced in Roman law and later codified in the Justinian Code, was revived in 17th century England through the writings of Sir Mathew Hale and became entrenched in American law in the nineteenth century. The doctrine's remarkable endurance over the centuries now brings its antimonopolistic overtones and human rights underpinnings not only to American law but worldwide,This casebook, now in its 3rd edition, provides the first systematic approach to the study of the doctrine, which is now rapidly evolving as courts and legislatures have extended its reach from waterways to wildlife, water rights, groundwater, beaches, funding decisions affecting natural resources, and even the atmosphere. Pathbreaking recent cases are from a wide variety of jurisdictions, including the Pennsylvania Supreme Court, the Netherlands Supreme Court, the Columbia Constitutional Court, and in courts in India and Pakistan. In a time in which the world is in the throes of global pandemic and intensifying climate disasters, the public trust doctrine offers an ancient anchor to support sovereign obligations to ensure access to and protection of public resources. In doing so, it provides a steadying force for government accountability.This casebook is an entry into this dynamic and consequential area of environmental and natural resources law. At less than 550 pages, we believe it serves as an ideal upper division course for students interested in exploring sovereign rights and obligations to increasingly scarce resources in the 21st century. Its rich history and considerable flexibility provides an ideal vehicle for examining issues like the role of courts and legislatures and their obligations to preserve and protect the planet for posterity. The 3rd edition of the book includes landmark decisions, extensive commentary, and a substantial bibliography of the considerable literature on the public trust doctrine. We include here the tables of contents, cases, and commentary and an introductory chapter