The General rules of interpretation contained in Article 31 of the Vienna Convention on the Law of Treaties do not only apply to treaties; they also apply to the constitutions of International Organizations. This paper argues that a textual application of the VCLT that interprets an IO‘s constitution “in good faith in accordance with the ordinary meaning to be given to the terms of the treaty in their context“ without applying an extended teleological approach to the constitution‘s “object and purpose“ compromises its ability to behave as an organization with values and practices that reflect contemporary expectations of accountability. An extended teleological approach to constitutional interpretation is the extension of the doctrine of implied powers to implied obligations, which are obligations that can be necessarily implied from an IO’s constitution where there is a close connection between the obligation and one or more of its generic functions or institutional purpose.