Per Wikipedia the Vienna Convention on the Law of Treaties (or VCLT) is a treaty concerning the customary 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 109 states as of May 2009;those that have not ratified it yet may still recognize it as binding upon them in as much as it is a restatement of customary law.

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