Eds. Olivier Corten, Pierre Klein. The 1969 and 1986 Vienna Conventions on the Law of Treaties are essential components of the contemporary international legal order. They aim at regulating what has become the main source of public international law and a crucial tool in inter-state relations. The Vienna Conventions codify to a significant extent the customary rules that pre-existed in the field, but also put forward innovative concepts, such as jus cogens. In spite of their importance, these two instruments had so far not been the object of a detailed commentary. These volumes fill that gap, by providing both international and national lawyers with an in-depth analysis of each provision of both Conventions. The structure of each commentary is essentially uniform, with the first part dedicated to the exposition of that provision's object and purpose and to the assessment of its customary status. The second part of each commentary deals with the main issues of interpretation raised by the provision in question. Extensive reference is made to the travaux preparatoires of both Conventions, including the work of the UN International Law Commission and the proceedings of the 1969 and 1986 diplomatic conferences, and to practice both prior to and following the adoption of the Conventions. The 90 + authors who contributed to the book come from twenty different countries and include some of the most respected experts in international law.