The Vienna Convention on the Law of Treaties, which entered into force in 1980, has been adopted at this writing by some eighty States, i.e. under half of the membership of the United Nations; and the States not party include a variety of States large and small, including such major States as the United States of America, China, Brazil, India and Pakistan. It nevertheless has been treated more than once by the International Court of Justice as expressive of customary international law binding upon States parties and non-parties alike. Thus in the case concerning the Territorial Dispute (Libyan Arab Jamahariya/Chad), the Court held:

In the case concerning Maritime Delimitation and Territorial Questions between Qatar and Bahrain: Jurisdiction and Admissibility, the Court applied (or, it may be argued, misapplied) the Vienna Convention's provisions on the interpretation of treaties to determine the rights of the parties to the dispute though neither Bahrain nor Qatar was party to the Convention.