The Vienna Convention on the Law of Treaties (VCLT) is an international agreement regulating treaties between states. Known as the "treaty on treaties", it establishes comprehensive rules, procedures, and guidelines for how treaties are defined, drafted, amended, interpreted, and generally operated. An international treaty is a written agreement between international law subjects reflecting their consent to the creation, alteration, or termination of their rights and obligations. The VCLT is considered a codification of customary international law and state practice concerning treaties. The convention was adopted and opened to signature on 23 May 1969, and it entered into force on 27 January 1980. It has been ratified by 116 states as of January 2018. Some non-ratifying parties, such as the United States, have recognized parts of it as a restatement of customary international law. The VCLT is regarded as one of the most important instruments in treaty law and remains an authoritative guide in disputes over treaty interpretation. History The VCLT was drafted by the International Law Commission (ILC) of the United Nations, which began work on the convention in 1949. During the 20 years of preparation, several draft versions of the convention and commentaries were prepared by special rapporteurs of the ILC, which included prominent international law scholars James Brierly, Hersch Lauterpacht, Gerald Fitzmaurice, and Humphrey Waldock. In 1966, the ILC adopted 75 draft articles, which formed the basis for its final work. Over two sessions in 1968 and 1969, the Vienna Conference completed the convention, which was adopted on 22 May 1969 and opened for signature on the following day. Content and effects The convention codifies several bedrocks of contemporary international law. It defines a treaty as "an international agreement concluded between states in written form and governed by international law" and affirms that "every state possesses the capacity to conclude treaties." Article 1 restricts the application of the convention to written treaties between States, excluding treaties concluded between the states and international organizations or international organizations themselves. Article 26 defines pacta sunt servanda, Article 53 proclaims peremptory norm, and Article 62 proclaims Fundamental Change of Circumstance. The convention has been referred to as the "treaty on treaties" and is widely recognized as the authoritative guide regarding the formation and effects of treaties. Even those countries who have not ratified it recognize its significance. For example, the United States recognizes that parts of the Convention constitute customary law binding