Article 38 of the International Court of Justice (ICJ) Statute enumerates the sources of "international law"...
(a) international conventions, whether general or particular, establishing rules expressly recognized by contesting states;
(b) international custom, as evidence of a general practice accepted as law;
(c) the general principles of law recognized by civilized nations;
(d) … 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.
Public International Law
Private International Law
Foreign Law
Comparative Law