Expropriation and the Relationship between Treaties and General International Law

This chapter uses expropriation provisions in international investment treaties and approaches to the interpretation of such provisions in investment treaty arbitration to examine the relationship between treaties and general international law. The chapter highlights the influential role of customary international law for the interpretation of treaty references to ‘expropriation,’ as well as the role of the customary international law ‘police powers’ doctrine for the application of those provisions. It then explores the role that customary international law has played in limiting the scope of the concept of ‘expropriation’ to certain proprietary rights before examining the linkage between custom and treaties in assessing the conditions for lawful expropriation. Finally, the chapter examines the extent to which investment treaties themselves might influence the development of general international law, with specific focus on the development of rules relevant to compensation for expropriation under customary international law. The chapter illustrates that the intersection of treaty provisions and general international law rules related to expropriation is both complex and evolving.