This paper sets out to evaluate the extent to which the WTO Dispute Settlement System takes the case law of the European Court of Justice into account. The ECJ is in a particular position from the WTO jurisdictions' point of view, because the EU is a fully-fledged member of the organization. This entails that referring to the ECJ as a regular international court would lead to an issue of impartiality. For this reason, we will first establish that the WTO Panels and the Appellate Body regularly look for guidance or confirmation in the case law of other international jurisdictions. We will then compare those elements to the way the ECJ is referred to, both by the parties to WTO disputes, and by the WTO “judges”. The comparison will allow us to conclude that the ECJ is mainly seen as a domestic court, and not as a fellow international one, even when its case law is taken into account by the WTO's Panellists and AB Members. We will finally put this vision in the broader context of the interaction of law regimes.