This article argues that the use of principles in WTO dispute resolution is both necessary and desirable. However, Panels and the Appellate Body (WTO Tribunals) have often ignored principles or not clearly identified the legal basis for their use. This article establishes a framework for the use of principles (in particular principles of WTO law, principles of customary international law, and general principles of law) in WTO dispute settlement. Broadly, WTO Tribunals can use principles drawn from these categories to interpret WTO provisions, based on Article 3.2 of the DSU, and Articles 31 and 32 of the VCLT. This follows most directly from a teleological approach to interpretation, but principles also feature under subjective and textual approaches to interpretation. WTO Tribunals may also use certain principles in a non-interpretative manner. Indeed, this may be necessary, particularly to address procedural issues. Precisely how a principle may be used depends on its type, content and status.