Path to judicial activism? The use of “relevant rules of international law” by the WTO Appellate Body

The Appellate Body (AB) of the World Trade Organization (WTO) is currently under the concrete threat of ceasing its activities in the near future. This is the result of a series of unaddressed criticisms by some of the members of the organization, in particular the United States, regarding the alleged activist role that the AB has played. These criticisms involve a number of issues regarding interpretative practices developed by the organ. Against this backdrop, the present paper tackles the use of “relevant rules of international law” which are external to the WTO covered agreements, in particular through Article 31(3)(c) of the Vienna Convention on the Law of the Treaties, the provision codifying the so-called “principle of systemic integration”. It studies the reports in which reference to this provision was made and whether the use of non-WTO rules has been made in an expansive or limited way with respect to the mandate of the AB. It also assesses the reception of these reports by the WTO membership in the meetings of the Dispute Settlement Body. It is concluded that, while recourse to external sources under the VCLT provision could represent a potential source of expansion of the AB material applicable law in a way that could displease the WTO membership, the AB has transitioned from a progressive approach which marked the beginning of its functioning to a more narrow approach to the applicability of non-WTO sources in the more recent caselaw