International law sets out the rules that govern the relations between the members of international society, including sovereign States, international organizations, and individuals. These rules were mainly created by and for States, but nowadays they encompass more users and address far more issues.

The structure of the international legal order is fundamentally different from that of national legal systems. Besides the absence of a central legislative organ—that is, the equivalent of a national parliament—there is no international police or international judge as conceived in the domestic setting, and both enforcement and adjudication of international rules depend heavily on the consent of the States concerned.

International legal theory has long struggled with contemplating the nature of the international legal system. Theories such as formalism, positivism, or naturalism, which concern every category of law, have been complemented by schools that focus explicitly on international law, such as realism or policy-oriented approaches, as well as by more contemporary theories like critical legal studies (CLS), feminism, and third world approaches in international law (TWAIL).

There are different categories of norms in the international legal system; a common distinction could be between obligations of a contractual nature and obligations towards the international community as a whole (obligations erga omnes). In addition, although there is no formal hierarchy among the sources of international law, there is a certain hierarchy of international norms: jus cogens (norms from which there can be no derogation) and jus dispositivum (norms that are susceptible to derogation).