An international agreement in writing between two states (a bilateral treaty) or a number of states (a multilateral treaty). Such agreements can also be known as conventions, pacts, protocols, final acts, arrangements, and general acts. Treaties are binding in international law and constitute the equivalent of the municipal-law contract, conveyance, or legislation. Some treaties create law only for those states that are parties to them, some codify pre-existing customary international law, and some propound rules that eventually develop into customary international law, binding upon all states (e.g. the Genocide Convention). Federal states, colonial states, and public international organizations are sometimes also able to enter into treaty obligations. The Vienna Convention on the Law of Treaties (1969) defines in detail the rules relating to inter-state treaties and is itself generally considered to declare or develop customary international law in this area. Treaties are normally concluded by the process of ratification. See also high contracting parties; reservation; signature of treaty.
In the UK the power to make or enter into treaties belongs to the monarch, acting on the advice of government ministers, but a treaty does not become part of municipal law until brought into force by an Act of Parliament.