NOTE: Although the following article has not been revised for this edition of the Encyclopedia, the substantive coverage is currently appropriate. The editors have provided a list of recent works at the end of the article to facilitate research and exploration of the topic.

International law is the system of rules and principles governing relations at the interstate level. It originally developed in response to the needs of states but in recent times has grown to include international organizations and, to some extent, individuals.

International law as a systematic body of rules began in Europe in the seventeenth century. Before then, and from earliest history, rules existed governing the interrelations of various groups of people (Nussbaum 1958). But the rules were systematized in Europe only when the contacts among peoples became regular and frequent and the idea of a single ruler for all known society foundered. That...