International law may be defined as a body of law formed as a result of international customs, treaties, and organizations that governs relations among or between nations. International Customs are customs evolved over the centuries. Treaties and International Agreements are agreements between or among nations. International Organizations and Conferences are composed mainly of nations and usually established by treaty — for example, the 1980 Convention on Contracts for the International Sale of Goods, or CISG.
Legal systems are generally divided into common law and civil law systems. Common law systems are based on case law. These systems exist in countries that were once a part of the British Empire (such as Australia, India, and the United States). Stare decisis requires following precedent unless otherwise necessary. Civil law systems are based on codified law (statutes). Courts interpret the code and apply the rules without developing their own laws. Civil law systems exist in most European nations, in Latin American, African, and Asian countries that were colonies of those nations; Japan; South Africa; and Muslim countries.