This work presents a new perspective on the role of States as reciprocal trustees for the Oceans Public Trust. The concept of the oceans and navigable waters as held in public trust is examined from its origins in the 17th century North Sea fisheries controversy with particular regard to the arguments by Selden and Grotius pertaining to State jurisdiction over oceans and marginal sea areas. Those arguments manifest an underlying common principle of navigational freedom reflected in the parallel public trust development of public rights to fishing and navigation as protected and preserved within the Royal Prerogative jus publicum. The significance for the modern context is that the 1958 Geneva Conventions on the Law of the Sea, the 1982 United Nations Convention on the Law of the Sea and a myriad of other conventions now evidence an unstated but patent public trust in the communal responsibility of States within both the conventional and customary regime of the high seas, as well as in regimes for territorial seas and marginal sea areas as shared with extended coastal State jurisdictions. This book is intended to serve as a reference work for this somewhat arcane source of the Oceans Public Trust, and should prove a useful research source for those who study law of the sea.