How does the World Trade Organization (WTO) relate to the wider corpus of public international law? What, in turn, is the role of public international law in WTO dispute settlement? This paper aims at resolving these two difficult questions. No straightforward answers to them can be found in WTO rules. Yet answering them has major ramifications both for the WTO (is the WTO a largely “self-contained regime” or is it not?) and for international law (is the future of international law further fragmentation or increased unity?). This exercise will be conducted under the law as it stands today—that is, the law as it may be invoked at present before the WTO “judiciary” (panels and the Appellate Body). Of course, WTO members (viz., the WTO “legislator”) could clarify or change the relationship between WTO rules and other rules of international law. However, it is unlikely that such changes will occur any time soon. In part I, I examine the general relationship between public international law and WTO law. I then assess, more specifically, the role of public international law in WTO dispute settlement in part II and offer some conclusions in part III.