International customary investment law: story of a paradox

This chapter zeroes in on customary international law and examines the role played by this specific source of law in the development of international investment law. After a few considerations on the early phase of development of an international investment protection regime and the search for a customary international protection of aliens, this chapter shows how the maturation of investment protection has been achieved through treatification and a move away from customary law. It then turns to the paradox of the theory of the sources of investment law and demonstrates how the completion of treatification through bilateral investment treaties (hereafter BITs) has generated a return to customary international. It subsequently ventures into a few general critical remarks about the rebirth of customary international law from the standpoint of the theory of the sources of international law.