Conceptualising the Relationship between Jus Cogens and Erga Omnes Rules

Abstract Few concepts in international law have attracted as much attention or created as much controversy as jus cogens and erga omnes rules. This article attempts to show that jus cogens rules are rules of customary international law, and then to elucidate the relationship between these customary rules and the concept of erga omnes. This article explains that: in contrast to jus cogens rules, erga omnes rules may arise either as customary rules or through treaties; a jus cogens or erga omnes rule could apply to only a limited number of States; although jus cogens rules are necessarily erga omnes rules, erga omnes rules could exist which were not of a jus cogens character.