Following a three-year post-termination transition period to bring investor-state arbitration disputes, the investment protections afforded by Chapter 11 of the North American Free Trade Agreement (NAFTA) finally expired in June 2023. Chapter 11 was one of the most litigated, cited, commented, and copied investment treaties. An important, but largely ignored, part of its legacy is how the making of NAFTA Chapter 11 shaped its subsequent successful diffusion. Combining traditional legal assessment with computational text-as-data analysis, this article shows how the give and take during the negotiations generated buy-in on the part of Mexico and Canada and emulation by Latin American countries who helped to spread NAFTA Chapter 11 language globally. The link between the making and diffusion of NAFTA Chapter 11 highlights the power of negotiated compromise: sharing the pen with others may sometimes be the most effective way to write the rules that come to shape the world.

Treaty obligations to afford foreign investors a minimum standard of treatment (MST) and/or fair and equitable treatment (FET) are hallmarks of international investment law. However, the relationship between such treaty-based obligations and customary international law has been the subject of considerable debate. In the North American Free Trade Agreement (NAFTA) context, the majority tribunal decision and dissenting opinion in Clayton and Bilcon of Delaware Inc. v Government of Canada (Bilcon) reflect ongoing disagreement regarding the threshold for breach of the MST under NAFTA Article 1105. This article charts NAFTA investment tribunals’ decisions regarding FET claims under Article 1105 and the development of the customary international MST on which that provision is based, in particular, the prohibition on arbitrary treatment. It argues that the majority in Bilcon applied an inappropriately low threshold in finding a breach of Article 1105, which could represent a new and unwelcome direction in NAFTA Chapter 11 jurisprudence.