Article 15 Vienna Convention on the Law of Treaties

Consent to be bound by a treaty expressed by accession

The consent of a State to be bound by a treaty is expressed by accession when:

(a) the treaty provides that such consent may be expressed by that State by means of accession;

(b) it is otherwise established that the negotiating States were agreed that such consent may be expressed by that State by means of accession; or

(c) all the parties have subsequently agreed that such consent may be expressed by that State by means of accession.

See also: Article 14 Vienna Convention on the Law of Treaties