One of the challenges of conducting research in this area is that there is no one central body that creates public international law and therefore no clear hierarchy in terms of the sources to rely on.
Researchers often look to two main authorities to identity sources of international law, the Statute of the International Court of Justice and the Restatement of the Law, Third: Foreign Relations Law of the United States. Sources considered and listed there create the framework for the practice of international law. This guide will help you track down those materials as considered below.
Understanding the differences between the practice of international law and other national systems is an important first step in order to better target helpful results in a challenging research environment. As you will see, starting with secondary sources is often the most efficient way to find the answers you are after.
The Statute of the International Court of Justice, Article 38(1) states:
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. [emphasis added]
The Restatement (Third) of Foreign Relations Law of the United States sets out the sources of international law in section 102 as follows:
(1) A rule of international law is one that has been accepted as such by the international community of states
(a) in the form of customary law;
(b) by international agreement; or
(c) by derivation from general principles common to the major legal systems of the world.
Section 103, which deals with the evidence of international law, states the following:
(2) In determining whether a rule has become international law, substantial weight is accorded to
(a) judgments and opinions of international judicial and arbitral tribunals;
(b) judgments and opinions of national judicial tribunals;
(c) the writings of scholars;
(d) pronouncements by states that undertake to state a rule of international law, when such pronouncements are not seriously challenged by other states. [emphasis added]