This chapter explores the availability of the customary defence of countermeasures to investment disputes brought before investor-state arbitral tribunals. It scrutinises the tribunals’ reasoning and the parties’ arguments in the cases of Archer Daniels Midland, Corn Products International and Cargill. It discusses their approach to the customary requirements for a lawful countermeasure and to the limits of their own jurisdiction ratione materiae and ratione personae. The chapter aims to discern firstly, whether CIL or the text of current investment treaties precludes responding states from invoking the defence of countermeasures in the context of an investment dispute. In this context, the chapter also offers some insights into the approach of arbitral tribunals to the customary requirements for the successful invocation of countermeasures. Secondly, it discusses whether the subject-matter and personal jurisdiction of arbitral tribunals precludes the tribunals from examining and applying the defence of countermeasures. The chapter argues that CIL does not preclude the applicability of countermeasures to investment disputes. It further argues that current investment treaties do not exclude, explicitly or implicitly, the defence of countermeasures.