The Vienna Formula is a standard final-clause formulation used in multilateral treaties to define which entities are eligible to sign, ratify, or accede. It takes its name from the 1969 Vienna Convention on the Law of Treaties, whose Article 81 opens participation to all States Members of the United Nations or of any of the specialized agencies or of the International Atomic Energy Agency or parties to the Statute of the International Court of Justice, and any other State invited by the General Assembly of the United Nations to become a party.
The formula serves a practical diplomatic function: it provides an objective, depositary-administrable test for treaty eligibility without forcing the depositary (usually the UN Secretary-General) to adjudicate contested questions of statehood. By relying on prior UN membership decisions, it outsources the political judgment about what is a state to the General Assembly and the specialized agencies.
The Vienna Formula is generally considered more restrictive than the all States formula (which opens treaties to any state) but less restrictive than instruments limited to UN members only. It has been used in numerous codification treaties drafted by the International Law Commission, including the 1961 Vienna Convention on Diplomatic Relations and the 1963 Vienna Convention on Consular Relations.
In practice, the formula has historically excluded entities whose statehood is contested or whose UN status is blocked — for example, Taiwan, Kosovo, or Palestine before its 2012 upgrade to non-member observer state. The 'invitation' clause acts as a residual safety valve allowing the General Assembly to extend participation case by case.
For delegates drafting treaty texts, choosing between the Vienna Formula, the all States formula, and bespoke participation clauses is a substantive negotiating decision with consequences for universality and political signaling.
Example
When the 1969 Vienna Convention on the Law of Treaties was opened for signature, its Article 81 applied the Vienna Formula to determine eligible state parties.