According to the Statute of the International Court of Justice art. 38, June 26, 1945, 59 Stat. 1055, 33 U.N.T.S. 993:
Treaties – international conventions, whether general or particular, establishing rules expressly recognized by the contesting States;
Customary international law – international custom, as evidence of a general practice accepted as law;
General principles of law – the general principles of law recognized by civilized nations;
Judicial decisions and teaching of “publicists” – judicial decisions and the teachings of the most highly qualified publicists of the various nations, as subsidiary means for the determination of rules of law.