In this paper presented at the Joint Study Institute in Oxford, Michael Bowman traces the history of international law, with its basis in custom, and identifies the late Nineteeth century as the period when multi-lateral treaties became commonplace. He considers whether such treaties, which were essentially static in nature, provide a suitable framework for the Twenty-first century global community. However, since the Vienna Convention, treaties have become dynamic as they now incorporate mechanisms for continuous monitoring and review of treaty obligations.