Vienna Convention on the Law of Treaties

The 1969 treaty on treaties, codifying how international agreements are made, interpreted, and ended

Overview

Drafted by the International Law Commission and concluded in Vienna in 1969, the convention entered into force in 1980 and sets out the basic rules of treaty law. It codifies pacta sunt servanda, the principle that treaties in force must be performed in good faith, provides the standard rules of interpretation according to ordinary meaning, context, and object and purpose, and governs reservations, invalidity, termination, and fundamental change of circumstances. It also gave formal recognition to jus cogens by declaring void any treaty conflicting with a peremptory norm. Even states that have not ratified it, including the United States, treat much of it as customary law.