There is no central international body that creates public international law; it is created by several sources.
The Charter of the United Nations is the establishing document for the International Court of Justice (ICJ) as the principal judicial organ of the UN. Article 38(1) of the Statute of the International Court of Justice lists the sources that the ICJ uses to resolve disputes as follows:
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 recognised 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.