1. The Court, whose function is to decide in accordance with international law such disputes as are submitted to it, shall apply:
a. international conventions, whether general or particular, establishing rules expressly recognized by the 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. subject to the provisions of Article 59, 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.
Vienna Convention on the Law of Treaties sets out the structure and rules of treaties.
Issues in treaty research
Commentary on the 1969 Vienna Convention on the Law of Treaties / by Mark E. Villiger. KZ1301.094.2012
The Oxford guide to treaties / edited by Duncan B. Hollis. 1st ed. Oxford, U.K. : Oxford University Press, 2012. KZ1301 .O94 2012