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Public International Law: Sources of International Law

This guide will help you find resources for researching public international law.

Teachings of 'Highly Qualified Publicists'

The writings of jurists are important in describing and analysing evolving norms and identifying general principles of law. In the absence of decisions of international tribunals, the body of international legal doctrine depends on the articulation of jurisprudence in books and journal articles. 

(Source: Gillian Triggs, International Law: Contemporary Principles and Practices (LexisNexis, 2nd ed, 2011) 

See Sivakumaran, Sandesh, 'The Influence of Teachings of Publicists on the Development of International Law' (2017) 66 International and Comparative Law Quarterly 1-37. Available on open access at SSRN. 

General Principles of Law

The 'general principles of law as recognised by civilized nations' have been traditionally recognised by courts as a source of international law, using judicial reason and logic to abstract the normative rule. See for example the decision of the PCIJ in the Chorzow Factory (Indemnity) case (1928) PCIJ Series A No 17

(Source: Gillian Triggs, International Law: Contemporary Principles and Practices (LexisNexis, 2nd ed, 2011) .

Online Encyclopaedias

Oxford Bibliographies Online - International Law  (University of Melbourne staff and students access only) provides authoritative encyclopedic entries and annotated bibliographies on a range of topics such as general customary law and general principles of law.

The Max Planck Encyclopedia of Public International Law (University of Melbourne staff and students access only) contains comprehensive and authoritative overviews of all aspects of international law. Entries are arranged alphabetically by topic under broad subjects such as sources of international lawcustomary international law, general principles of international law, state practice and the law of treaties

Sources of International Law

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 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.

Further information regarding these sources is provided in this Research Guide under the headings and links listed below:

  • International conventions (Treaties)
  • International Custom (see box on this page)
  • General principles of law ​(see box on this page)
  • Case law 
  • Teachings of Highly Qualified Publicists ​(see box on this page)



International Custom

Customary international law consists of rules that derive from "a general practice accepted as law" and exist independent of treaty law. Unlike treaties, customary international law is not written. To prove that a certain rule is customary, it has to be shown that it is reflected in state practice and that the international community believes that such practice is required as a matter of law.

Prior to the practice of negotiating multilateral treaties after WWII, international law consisted primarily of customary rules. Custom has evolved through a long historical process by which state practices and recognition of the binding character of those practices have become normative rules.  The rationale for custom is that it rests on the consent of sovereign or equal states. The creation of custom can be slow and its content uncertain, and it has been replaced to a large extent by multilateral treaties, but custom nontheless continues to contribute significantly to international law.

The criteria for the identification of custom were articulated in the North Sea Continental Shelf Cases in 1969 (FRG v Denmark; FRG v The Netherlands (1969) ICJ Reports 3). These elements of custom are:

  • objective evidence of state practice; and
  • the subjective element of opinio juris (as formulated by the Court in the UK case West Rand Central Gold Mining Co v The King [1905] 2 KB 391.

The work of the International Law Commission (ILC) provides authoritative evidence of customary law.

(Source: Gillian Triggs, International Law: Contemporary Principles and Practices (LexisNexis, 2nd ed, 2011) .

The following will help you research international custom:

See also: