Peremptory norm

Also called jus cogens (L. "compelling law"), a peremptory norm is a fundamental principle of international law considered to have acceptance among the international community of states as a whole. Unlike ordinary customary law that has traditionally required consent and allows the alteration of its obligations between states through treaties, peremptory norms cannot be violated by any state. Under the Vienna Convention on the Law of Treaties, any treaty in violation of a peremptory norm is null and void.

The number of peremptory norms is considered limited but not exclusively catalogued. Included are prohibitions on waging aggressive war, piracy, genocide, slavery, and torture.

Despite the seemingly clear weight of condemnation of such practices, some critics disagree with the division of international legal norms into a hierarchy. There is also disagreement over how such norms are recognized or established. The relatively new concept of peremptory norms is at odds with the traditionally consensual nature of international law considered necessary to state sovereignty. However, sovereignty has never truly been an absolute concept and limitations upon it are increasingly supported.