Editors' Summary: The public trust doctrine is an amorphous legal concept that generally provides that states hold certain submerged land and tidelands in trust for their citizens. In Phillips Petroleum Co. v. Mississippi, the Supreme Court held that state ownership of lands subject to the public trust includes nonnavigable lands that are subject to the influence of the tide. This Comment analyzes the Court's decision, which could bring millions of acres of wetlands within the reach of the public trust. The author traces the development of the public trust doctrine and the impact of the Court's decision on the scope of the doctrine. The author observes that the Court, in adopting tidal influence as the test for application of the public trust doctrine, may have recognized the difficulties courts have had interpreting the traditional navigability test. The decision also provides an important policy statement in favor of the state's role in wetlands protection.