The ICJ has confirmed that, on the one hand, the customary status of the general rule of treaty interpretation in the Vienna Convention on the Law of Treaties makes it applicable to the constituent instruments of all international organizations, but, on the other hand, constituent instruments are ‘treaties of a particular type’ with special considerations. This article examines the resultant implication that the Court adopts an approach to constituent instrument interpretation that supplements or modulates the approach provided for in the Convention. In doing so, it examines both the Advisory Opinions that respond to direct questions of constituent instrument interpretation, as well as Opinions and Judgments in which a question of constituent instrument interpretation is incidental to a dispute with respect to another treaty or general international law. The article identifies nine interpretative propositions used by the Court: (1) sufficiently clear text is conclusive; (2) the text cannot be nullified; (3) working documents (travaux préparatoires) afford auxiliary interpretation; (4) consistent practice precludes contrived interpretation; (5) to be consistent, practice need not be unanimous; (6) consistent institutional practice is determinative; (7) purpose can supplement text, but cannot contradict practice; (8) practice is interpretation, unless institutionally overruled; and (9) interpretation cannot be gratuitous. It is argued that to the extent the Court diverges from the Convention, it in fact allows for a more efficient and effective approach to constituent instrument interpretation and accords institutional practice particular prominence.
