The Sources of Public International Law

International Law also known as “Law of Nations” or “Public International Law”, is the name of a body of rules which regulate the conduct of sovereign states in their relations with one another. Sources of Public International Law include treaties, international customs, general principles of law as recognised by civilized nations, the decisions of national and lower courts, and scholarly writings.

They are the materials and processes out of which the rules and principles regulating the International Community (a phrase used in geopolitics and international relations to refer to a broad group of people and governments of the world) are developed. They have been influenced by a range of political and legal theories.

The term “sources of Public International Law” is used to mean two things: first, the actual materials determining the rules applicable to a given international situation (the material sources), and second, the legal methods creating rules of general application (the formal sources).

The Sources of Public International Law

There is no central international body that creates public international law; it is created by several sources. The International Court of Justice (ICJ) is the principal legal organ of the United Nations. Under Article 93 of the UN Charter, all UN member states are ipso facto parties to the ICJ Statute, but they are not required to submit any case to it except in cases where they have consented or promised to do so. The ICJ only has jurisdiction to decide cases that states consent to submit to it for decision. That consent can take the form of binding treaties or declarations of varying scope. Article 38 of the Statute of the International Court of Justice (ICJ) lists the sources of Public International Law and states the following:

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 teaching of the most highly qualified publicists of the various nations, as subsidiary means for the determination of rules of law.

2. This provision shall not prejudice the power of the Court to decide a case ex aequo et bono, if the parties agree thereto”.

This Article 38 of the Statute of the International Court of Justice (ICJ) lists the traditional sources of Public International Law, the actual legal materials that the ICJ has to apply to international disputes. According to this Article 38, these sources are of two types: the primary sources that are represented by the international conventions, international custom and general principles of law; and the subsidiary sources that are represented by the decisions of courts and the opinions of legal scholars. Moreover, this Article 38 lists “ex aequo et bono” (equity) as an alternative source of Public International Law applied by the Court if the parties agree thereto. However, in addition to these traditional sources, there are contemporary sources, such as the acts of the international organisations. Let’s now have a look at the three main sources of Public International Law.


The term “treaty” is used as a generic term embracing all kinds of international agreements which are known by a variety of different names such as, conventions, pacts, general acts, charters, statutes, declarations, covenants, protocols, as well as, the name agreements itself. A treaty may be defined as an international agreement concluded between States in written form and governed by International Law.

The law-making treaties constitute a primary source of International Law. Since the middle of the nineteenth century, there has been an astonishing development of law-making treaties. The rapid expansion of this kind of treaties has been due to the inadequacy of customs in meeting the urgent demands arose from the changes which have been transforming the whole structure of international life. Law-making treaties have been concluded to regulate almost every aspect concerning the international community. Examples of important treaties are: the Charter of the United Nations, the four Geneva Conventions of 1949, the Vienna Convention on Diplomatic Relations of 1961, the International Covenant on Civil and Political Rights of 1966, the Convention on the Law of the Sea of 1982, and the Outer Space Treaty of 1967.

In contrast with the process of creating law through custom, treaties are a more modern, more deliberate and speedy method. They are of growing importance in International Law. Their role in the formation of new rules of International Law increases day after day. Today, the law-making treaties are considered the most important primary source of Public International Law.

International Custom

Article 38 of the Statute of the ICJ refers to an International Custom as evidence of a general practice accepted as law. This definition comprises of two elements: a general practice and its acceptance as law. These two elements are necessary for the formation of customary international law. The first element, the behavioural or objective element, requires a recurring consistent action or lack of action by States, which is indicated by such activities as official statements or conducts, legislative or administrative action, court decisions and diplomatic behaviours or correspondence. The second element (the psychological or subjective element) entails the conviction that in similar case such a practice is required or permitted by international law. In this sense, international customs may be defined as practices or usages which have been observed by a large number of States over a lengthy period of time and considered by them to be legally obligatory.

General Principles of Law

Article 38 of the Statute of the ICJ refers to “the general principles of law recognized by civilized nations” (all nations are now considered as civilised) as a primary source of International Law. This source is listed the third after international conventions and international customs. The Court shall apply the general principles of law in cases where treaties and customs provide no rules to be applied.

There is no agreement on what the term “general principles of law” means. Some say it means general principles of international law; others say it means general principles of national law. Actually, there is no reason why it should not mean both; the greater expansion in the meaning of this term, the greater chance of finding rules to fill the gaps in Treaty Law and Customary Law.

There are various opinions as to the origin of the general principles of law. Some regard them as being originated from the Natural Law which underlies the system of International Law and constitutes the criteria for testing the validity of the positive rules. Others regard them as stemmed from the national legal systems (Positive Law) and have been transplanted to the international level by recognition.