VCLT

The Vienna Convention on the Law of Treaties (VCLT) is the principal international treaty that codifies the rules governing treaties between states, and, to a more limited extent, international organizations. Adopted in 1969 at a United Nations conference in Vienna and entering into force in 1980, it provides a comprehensive framework for how treaties are formed, interpreted, amended, suspended, and terminated. The Convention has achieved broad acceptance and is widely regarded as the foundational source of contemporary treaty law.

Core principles and provisions cover several areas. The doctrine of pacta sunt servanda, that treaties must be observed in good faith, underpins the enforceability of treaty obligations. The VCLT sets rules for interpreting treaties, emphasizing the ordinary meaning of terms, the treaty context, and applicable subsequent practice, supplemented by other means when necessary. It also regulates reservations to treaties and the conditions under which other parties may object to or disallow those reservations. It provides mechanisms for the modification, termination, or suspension of treaties, including through consent, breach, or changing circumstances.

The Convention also addresses the invalidity of consent to be bound by a treaty, outlining grounds such as error, corruption, or duress. A key provision is the prohibition on treaties that violate peremptory norms of general international law (jus cogens). The VCLT thus functions as the framework within which most international treaty relations are created, interpreted, and regulated, and it is routinely applied by international courts and tribunals in disputes over treaty obligations.