This chapter examines the state of international investment law that exists in the absence of an applicable treaty, as that law remains an important foundation for the international law governing investments. One of the purposes of law is to protect the legitimate interests of persons, groups, and states, and to provide a mechanism for resolving disputes when those interests are in conflict. In any international investment transaction, there are three primary parties in interest: the investor, the host country in which the investment is made, and the home country of the investor. Each party ordinarily uses laws and legal devices to advance its perceived interests. The chapter then explores the sources of international law, as well as customary international law and general principles of law governing international investment. It also looks at customary international law on expropriation and breach of state contracts.
