It is now standard in contemporary international law commentary to note that the latter part of the twentieth century has seen a move away from the traditional understanding of international law as fundamentally based on the consent of states. As just two examples, customary international law has in some contexts become more influential than treaties and human rights obligations are now recognized as often binding states even when they have signed no treaty acknowledging their existence. Treaty interpretation, by contrast, has remained focused upon the parties to a treaty, with even textualist approaches to treaty interpretation justified as the best means of ascertaining the intent of the contracting states. The purpose of the present article is to highlight the existence of a subset of treaties for which even a teleological approach to interpretation fails to capture the central importance for the treaty of entities other than the contracting states. These ‘power-conferring treaties’ do not merely entrust tribunals with the power to effectively fashion the means by which a treaty's goals should be achieved. To varying degrees, they grant control of the treaty itself, including, at times, both its enforcement and the very meaning of its terms, to entities other than the contracting states. As a result, the traditional emphasis in treaty interpretation on the ‘object and purpose’ of the treaty, and the precise language in which the treaty is written, will fail to generate an interpretation that faithfully captures the manner in which the treaty genuinely functions. The article then illustrates the potential impact of the power-conferring nature of a treaty through an analysis of the meaning of the term ‘investment’ in the International Convention for Settlement of Investment Disputes. This is one of the most controversial topics in contemporary international investment law, with an enormous impact upon the jurisdiction of ICSID arbitral tribunals. It is argued that recognizing the power-conferring nature of the ICSID Convention provides an enhanced understanding of the way in which this term should be interpreted.