Customary International Law

Abstract:     
In order to be considered customary international law, a provision or prohibition must be (1) state practice -- evidenced by long-term, widespread compliance by many states; and (2) opinio juris -- states' belief that compliance with a standard is not merely desired, but required by international law. The persistent objector doctrine permits states that expressly and persistently object to a customary international norm from its inception to not be held to it. The essay analyzes a ten-year study completed by the International Committee of the Red Cross on customary international humanitarian law and traces a disagreement between the study's authors and legal advisors from the U.S. government over various aspects of the methodology used to identify the customary international humanitarian law. The study is instructive on the various issues that arise during the attempted classification of such norms as well as the role that governments play in the process. While governments may commit acts that violate these norms, it is not necessarily the case that they disagree with the existence of the norm. The essay concludes that even with all the difficulties involved in identifying the emergence of customary international law, courts still turn to those norms in specific conflicts, and states do accept in general that customary international law is a valid type of law.

Keywords: custom, customary international law, state practice, opinio juris, International Committee of the Red Cross Customary International Humanitarian Law Study

Accepted Paper Series