The Vienna Convention on the Law of Treaties (or VCLT) is a treaty concerning the international law on treaties between states. It was adopted on 22 May 1969 and opened for signature on 23 May 1969. The Convention entered into force on 27 January 1980. The VCLT has been ratified by 113 states as of January 2013. Some countries that have not ratified the Convention recognize it as a restatement of customary law and binding upon them as such.