Investment treaties are complex international economic agreements. Th ey are crafted to provide predictability, and security to foreign investors, while protecting the national interests of host countries and remaining legitimate in the eyes of civil society. Th ese competing objectives are variously expressed through principles developed in international customary law, as well as in a plethora of free trade and bilateral investment treaties. Th ese customary and treaty laws prescribe, not always consistently, who is an investor, what is an investment, and what is an expropriation. Th ey highlight sometimes disparate standards of treatment that states are required to accord to foreign investors, such as national treatment, the minimum standards of justice, and fair and equitable treatment. Th ey also provide for the protection of the national interests of diff erent states, such as essential national security, public health, and protection of the environment. Th ey, more recently, echo the sentiments of civil society by providing, or referencing, transparency and public input. In the event of a confl ict, these treaties rely primarily on investor–state arbitration to resolve claims brought by foreign investors against host states, but again with variable results.