One of the defining characteristics of the modern global economy is the ease with which capital flows across international borders. While international trade involves an exchange at the border of money for goods or services and is usually a relatively short term transaction, international capital movements generally involve an investor of one country who establishes an investment inside the territory of another country for an extended period of time, sometimes decades. Such investment often includes not only capital, but also intellectual property rights, concession agreements, tangible property, real estate, and other assets. Once invested, it becomes subject to the regulatory authority of the country where it is situated, putting the foreign investor at risk not only of adverse economic circumstances in that country, but also of adverse government action, often referred to as sovereign risk. This sovereign risk includes, among other things, expropriation, currency exchange controls, discriminatory legislation, damage from wars, riots, and other civil disturbances, failure to protect, breach of investment agreements, and denial of justice in local courts. International investment law comprises the study of the rules adopted under international law to protect foreign investment against sovereign risk. These rules may be found in a network of more than 2,600 bilateral and multilateral treaties concluded worldwide, as well as in principles of customary international law. Such rules are enforceable in a variety of ways, including a system of international arbitration that has yielded hundreds of arbitral decisions awarding billions of dollars in compensation to investors.