The “Externalities” of Joint Interpretations in Investment Arbitration: Learning from the Past

The joint interpretation mechanism is gaining increasing attention in the recent practice and study of international investment law. In the past, the NAFTA Free Trade Commission exercised this interpretative authority by issuing the controversial Notes of Interpretation which limit the scope of fair and equitable treatment (FET) to customary international law. While much has been debated about the legitimacy of the Notes in the context of NAFTA arbitration, this article examines its influence on tribunals not bound by it (i.e. non-NAFTA tribunals). An extensive review of cases shows that non-NAFTA tribunals are generally cautious about directly applying the Notes to their own interpretation, while some followed NAFTA precedents shaped by the Notes. Considering the possible proliferation of the joint interpretation mechanism in the future, this article further examines the role of third states' joint interpretations in treaty interpretation through the lens of Articles 31 and 32 of the VCLT. © Koninklijke Brill NV, Leiden, 2023.