The Vienna Convention on the Law of Treaties
By the middle of the 20th century the customary international law of treaties had grown a fairly extensive body of rules. The problem was resolved by the adaptation of the Vienna Convention on the Law of Treaties
on 22 May 1969 (entered into force on 27 January 1980). The Convention is an essential component of the contemporary international legal order, it has been ratified by more than hundred states and some countries that have not ratified recognize it as a restatement of customary law and binding upon them as such.