The aim of this article is to shed light on the legally important and politically sensitive question of the respective responsibility of the European Union (EU) and its member states for the performance of World Trade Organization (WTO) obligations. Specifically, it seeks to challenge two propositions often found in the literature on the basis of a rigorous analysis of WTO dispute settlement practice. First, the claim that the EU’s exclusive responsibility for breaches of WTO law by its member states has been widely accepted by other WTO members and dispute settlement organs is not well grounded in existing WTO jurisprudence nor supported by recent post-Lisbon WTO dispute settlement practice. Second, and contrary to what some EU law scholars appear to suggest, what has been decisive in assigning international responsibility in the WTO is not the division of external (treaty-making) competences between the EU and its member states but, rather, the allocation and exercise of internal (treaty-infringing/treaty-performing) competences. In this sense, the Treaty of Lisbon has not fundamentally changed how the issue of EU/member states international responsibility is to be approached in the WTO, insofar as the EU member states remain members of that organization in their own right. With this in mind, a redefined ‘competence/remedy’ model is put forward to help us untangle ‘who is responsible’ to third parties for breaches of WTO law.