This Article examines the three most prominent uses of the term “object and purpose” within the Vienna Convention on the Law of Treaties and, in each instance, offers a new method for applying the term. First, the rule that a treaty be interpreted “in light of” its object and purpose requires a process of interpretation that oscillates between a treaty’s individual provisions and the logic of all its provisions as a whole. Second, for reservations, the term exists to preserve “rule coherence[,]” as that term has been developed by Professor Thomas Franck. Lastly, states are required upon signature not to “defeat” the object and purpose of a treaty, and this rule is best understood as a means of facilitating domestic legislative review of new treaties by preserving the status quo at the time of signature. In sum, this Article examines a term of art that has perplexed scholars and practitioners for decades, and, in three specific contexts, it offers an understanding of the term refined beyond what other writers have offered.