This series features works on substantial topics in international law which provide authoritative statements of the chosen areas. Taken together they map out the whole of international law in a set of scholarly reference works and treatises intended to be of use to scholars, practitioners, and students. This book provides a guide to interpreting treaties properly in accordance with the modern rules for treaty interpretation which are codified in the Vienna Convention on the Law of Treaties. These rules now apply to virtually all treaties both in an international context and within many national legal systems where treaties have an impact on a large and growing range of matters. Lawyers, administrators, diplomats, and officials at international organisations are increasingly likely to encounter issues of treaty interpretation which require not only knowledge of the relevant rules but also how these rules have been, and are to be, applied in practice. There is now a considerable body of case law on application of the codified rules. This case law, combined with the history and analysis of the rules, provides a basis for understanding this most important task in the application of treaties internationally and within national systems of law. Any lawyer who ever has to consider international matters, and increasingly any lawyer whose work involves domestic legislation with any international connection, is at risk nowadays of encountering a treaty provision which requires interpretation, whether the treaty provision is explicitly in issue or is the source of the relevant legislation. This expanded edition includes consideration of a range of recent cases, takes account of relevant work of the International Law Commission, and has new material addressing matters raised in the growing body of literature on treaty interpretation.