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International trade law is overwhelmingly treaty-based. In the traditional sense of ‘sources of law’, the World Trade Organization (WTO) treaty is the unique source of WTO law, for practical purposes. Customary law and general principles play (p. 1048) virtually no role as independent sources of substantive law. But the WTO treaty, like any treaty, requires interpretation, and there are vexed questions about what we might call the ‘sources for treaty interpretation’. What materials other than the treaty text may be used in interpreting the treaty? And how are they to be used? These questions arise both for materials internal to the WTO system, such as Committee decisions or the documents prepared by the Secretariat as part of the negotiating process, and for external materials such as customary law, general principles, and most controversially these days, non-WTO treaties.


Reproduced by permission of Oxford University Press