Peremptory norm

A peremptory norm (also called jus cogens) is a fundamental principle of international law that is accepted by the international community of states as a norm from which no derogation is permitted. Thought to be so fundamental that it even invalidates rules drawn from treaty or custom, "norms of this character, therefore, cannot be derogated from by the will of the contracting parties."

Article 53 of the Vienna Convention on the Law of Treaties defines jus cogens norms as those that are "accepted and recognized by the international community of states as a whole as a norm from which no derogation is permitted and which can be modified only by a subsequent international norm of the same character." This means that even states objecting to the norm are bound by it, and any treaty or international agreement conflicting with a peremptory norm is void.

There is no universal agreement regarding precisely which norms are jus cogens nor how a norm reaches that status, but it is generally accepted that jus cogens bans genocide, maritime piracy, enslaving in general (i.e. slavery as well as slave trade), wars of aggression and territorial aggrandizement, and generally as well torture, and refoulement.