The Commentary on the Vienna Convention on the Law of Treaties provides an in-depth article-by-article analysis of all provisions of the Vienna Convention. The texts are uniformly structured: (I) Purpose and Function of the Article, (II) Historical Background and Negotiating History, and (III) Elements of the Article. The Vienna Convention on Treaties between States and IOs and between IOs is taken into account where appropriate. In sum, the present Commentary contains a comprehensive legal analysis of all aspects of the international law of treaties. Where the law of treaties reaches into other fields of international law, e.g. the law of state responsibility, the relevant interfaces are discussed and contextualized. With its focus on international practice, the Commentary is addressed to academia, as well as to practitioners of international law.