Public International Law - International Law Sources

International Law Sources

Under article 38 of the Statute of the International Court of Justice, public international law has three principal sources: international treaties, custom, and general principles of law. In addition, judicial decisions and teachings may be applied as "subsidiary means for the determination of rules of law".

International treaty law comprises obligations states expressly and voluntarily accept between themselves in treaties. Customary international law is derived from the consistent practice of States accompanied by opinio juris, i.e. the conviction of States that the consistent practice is required by a legal obligation. Judgments of international tribunals as well as scholarly works have traditionally been looked to as persuasive sources for custom in addition to direct evidence of state behavior. Attempts to codify customary international law picked up momentum after the Second World War with the formation of the International Law Commission (ILC), under the aegis of the United Nations. Codified customary law is made the binding interpretation of the underlying custom by agreement through treaty. For states not party to such treaties, the work of the ILC may still be accepted as custom applying to those states. General principles of law are those commonly recognized by the major legal systems of the world. Certain norms of international law achieve the binding force of peremptory norms (jus cogens) as to include all states with no permissible derogations.