The 1969 Vienna Convention on the Law of Treaties, regulating treaties between States, lies at the heart of international law. This commentary interprets the Convention's 85 articles clearly and precisely. It covers such major topics as reservations to treaties, their interpretation and the grounds for terminating a treaty, for instance breach. Emphasis is placed on the practice of States and tribunals and on academic writings. It contains further sections on customary international law and the Convention's history while providing up-to-date information on ratifications and reservations. This commentary is a must for practitioners and academics wishing to establish the meaning and scope of the provisions of the Vienna Convention on the Law of Treaties.