Jus cogens literally means “compelling law.” It designates norms from which no derogation is permitted by way of particular agreements. It stems from the idea already known in Roman law that certain legal rules cannot be contracted out. Jus cogens is opposed to jus dispositivum, i.e., rules that yield to the will of the parties. In case of a contrary disposition of the parties, one can contract out of jus dispositivum but not out of jus cogens.