Sources of Law

Sources of Law

Sources of International Law

It is generally accepted that the sources of international law (international obligations) are listed in the Article 38(1) of the Statute of the International Court of Justice, which provides that the Court shall apply:

  • international conventions, whether general or particular, establishing rules expressly
    recognized by the contesting states;
  • international custom, as evidence of a general practice accepted as law;
  • the general principles of law recognized by civilized nations;
  • 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.


International conventions are generally referred to as treaties. Treaties are written agreements
between States that are governed by international law. Treaties are referred to by different
names, including agreements, conventions, covenants, protocols and exchanges of notes. If
States want to enter into a written agreement that is not intended to be a treaty, they often refer to it as a Memorandum of Understanding and provide that it is not governed by international law. Treaties can be bilateral, multilateral, regional and global.

The law of treaties is now set out in the 1969 Vienna Convention on the Law of Treaties which
contains the basic principles of treaty law, the procedures for how treaties becoming binding and enter into force, the consequences of a breach of treaty, and principles for interpreting treaties.

The basic principle underlying the law of treaties is pacta sunt servanda which means every
treaty in force is binding upon the parties to it and must be performed by them in good faith. The other important principle is that treaties are binding only on States parties. They are not binding on third States without their consent. However, it may be possible for some or even most of the provisions of a multilateral, regional or global treaty to become binding on all States as rules of customary international law.

There are now global conventions covering most major topics of international law. They are
usually adopted at an international conference and opened for signature. Treaties are sometimes referred to by the place and year of adoption, e.g. the 1969 Vienna Convention. If a State becomes a signatory to such a treaty, it is not bound by the treaty, but it undertakes an obligation to refrain from acts which would defeat the object and purpose of the treaty.

A State expresses its consent to be bound by the provisions of a treaty when it deposits an
instrument of accession or ratification to the official depository of the treaty. If a State is a
signatory to an international convention it sends an instrument of ratification. If a State is not a
signatory to an international convention but decides to become a party, it sends an instrument of accession. The legal effect of the two documents is the same. A treaty usually enters into force after a certain number of States have expressed their consent to be bound through accession or ratification. Once a State has expressed its consent to be bound and the treaty is in force, it is referred to as a party to the treaty.

The general rule is that a treaty shall be interpreted in good faith in accordance with the ordinary meaning to be given to the terms of the treaty in their context and in light of its object and purpose. The preparatory work of the treaty and the circumstances of its conclusion, often called the “travaux preparatoires”, are a supplementary means of interpretation in the event of ambiguity.


International custom – or customary law – is evidence of a general practice accepted as law
through a constant and virtually uniform usage among States over a period of time. Rules of
customary international law bind all States. The State alleging the existence of a rule of
customary law has the burden of proving its existence by showing a consistent and virtually
uniform practice among States, including those States specially affected by the rule or having the greatest interest in the matter. For example, to examine the practice of States on military uses of outer space, one would look in particular at the practice of States that have activities in space.

Most ICJ cases also require that the States who engage in the alleged customary practice do so
out of a sense of legal obligation or opinio juris rather than out of comity or for political reasons.

In theory, opinio juris is a serious obstacle to establishing a rule as custom because it is
extremely difficult to find evidence of the reason why a State followed a particular practice. In
practice, however, if a particular practice or usage is widespread, and there is no contrary State
practice proven by the other side, the Court often finds the existence of a rule of customary law. It sometimes seems to assume that opinio juris was satisfied, and it sometimes fails to mention it.

Therefore, it would appear that finding consistent State practice, especially among the States with the most interest in the issue, with minimal or no State practice to the contrary, is most important.

Undisputed examples of rules of customary law are:

  • giving foreign diplomats criminal immunity;
  • treating foreign diplomatic premises as inviolable;
  • recognizing the right of innocent passage of foreign ships in the territorial sea;
  • recognizing the exclusive jurisdiction of the flag State on the high seas;
  • ordering military authorities to respect the territorial boundaries of neighboring States; and
  • protecting non-combatants such as civilians and sick or wounded soldiers during international armed conflict.

General Principles of Law

General principles of law recognized by civilized nations are often cited as a third source of law.
These are general principles that apply in all major legal systems. An example is the principle
that persons who intentionally harm others should have to pay compensation or make reparation. General principles of law are usually used when no treaty provision or clear rule of customary law exists.

Subsidiary means for the determination of rules of law

Subsidiary means are not sources of law, instead they are subsidiary means or evidence that can be used to prove the existence of a rule of custom or a general principle of law. Article 38 lists only two subsidiary means – the teaching (writings) of the most highly qualified publicists
(international law scholars) and judicial decisions of both international and national tribunals if
they are ruling on issues of international law. Writings of highly qualified publicists do not include law student articles or notes or doctoral theses.

Resolutions of the UN General Assembly or resolutions adopted at major international
conferences are only recommendations and are not legally binding. However, in some cases,
although not specifically listed in article 38, they may be subsidiary means for determining
custom. If the resolution purports to declare a set of legal principles governing a particular area, if it is worded in norm creating language, and if is adopted without any negative votes, it can be
evidence of rules of custom, especially if States have in practice acted in compliance with its

Examples of UN General Assembly Resolutions which have been treated as strong
evidence of rules of customary international law include the following:

  • GAR 217A Universal Declaration of Human Rights (1948)
  • GAR 2131 Declaration on the Inadmissibility of Intervention in the Domestic Affairs of
    States and the Protection of their Sovereignty (1965) [Declaration on NonIntervention]
  • GAR 2625 Declaration on Principles of International Law Concerning Friendly
    Relations and Cooperation among States in Accordance with the Charter of the
    United Nations (1970) [Declaration on Friendly Relations]
  • GAR 3314 Resolution on the Definition of Aggression

Some of these resolutions have also been treated as subsequent agreement or practice of States on how the principles and provisions of the UN Charter should be interpreted.

In addition, Article 38 fails to take into account the norm-creating effect of modern global
conventions. Once the international community has spent several years drafting a major
international convention, States often begin in practice to refer to that convention when a problem arises which is governed by the convention – in effect treating the rules in the Convention as customary. Furthermore, if the Convention becomes universally accepted the provisions in the Convention may become very strong evidence of the rules of custom, especially if States which are not parties have also acted in conformity with the Convention. Examples of such conventions would be the 1959 Vienna Convention on Diplomatic Relations and the 1969 Vienna Convention on the Law of Treaties.

Hierarchy of norms

In theory there is no hierarchy among the three sources of law listed in Article 38 of the ICJ
Statute. In practice, however, international lawyers usually look first to any applicable treaty
rules, then to custom, and last to general principles.

There are two types of norms or rules – not previously discussed – which do have a higher status:

  • First, peremptory norms or principles of jus cogens are norms that have been accepted and
    recognized by the international community of States as so fundamental and so important that no derogation is permitted from them. Examples of jus cogens principles are the prohibitions against wars of aggression and genocide. A war of aggression is the use of armed force to take over another State or part of its territory. Genocide is the killing or other acts intended to destroy, in whole or in part, of a national, ethnical, racial or religious group.
  • Second, members of the United Nations are bound by the Article 103 of the United Nations Charter, which provides that in the event of a conflict between the obligations of members under the Charter – including obligations created by binding decisions of the Security Council – the Charter obligations prevail over conflicting obligations in all other international agreements.

Role of the International Law Commission (ILC)

The ILC was established by the UN in 1948. The 34 members of the ILC are elected by the
General Assembly after being nominated by member States. They possess recognized
competence and qualifications in both doctrinal and practical aspects of international law and the ILC reflects a broad spectrum of expertise and practical experience.

The mandate of the ILC is the progressive development and codification of international law. The ILC usually spends many years studying areas of international law before presenting draft articles to the General Assembly for adoption as a draft convention. The primary written products of the ILC aside from the draft articles themselves are the detailed periodic reports prepared by the Special Rapporteurs on each subject and the official commentary for each draft article.

Sometimes the official commentary to an ILC draft article or the RapporteurÂ’s report will indicate whether that draft article is intended to codify a rule of customary law or is intended to
progressively develop the law on that point. When the ILC Draft Articles are approved, they are
approved together with the official commentaries.

The official commentaries to ILC draft articles and the reports of the ILC and its rapporteurs can
be considered for two purposes. First, they are part of the travaux préparatoires when
interpreting a treaty related to the subject of the draft article. Second, they are the writings of
highly qualified publicists speaking in unanimity and therefore serve as a subsidiary means for
determining rules of customary law.

The Legal History of Sources of Law in English Common Law

This section provides an overview of Sources of Law in English Common Law

Sources of Internet Law and Practice framework for Developing New Law

Read, in this legal Encyclopedia, about the topic of this section, and, specially, about A Framework for Developing New Law.

Other Basic Elements of the International Law

International Legal Personality

It refers to the entities or legal persons that can have rights and
obligations under international law. Learn more about International legal personality here.

Sovereignty of States over Territory

Sovereignty imply that no other State can have formal political authority (at least, in theory) within that State. Learn more about Sovereignty of States over Territory here.

Jurisdiction of States

This section covers mainly the Principles of Jurisdiction, and Immunities from Jurisdiction.

Principles Governing relations between States

The general principles governing friendly relations between States are set out in UN General
Assembly Resolution 2625. Learn more about the principles governing relations between States here.

The Role of International Court of Justice (ICJ)

The jurisdiction of the International Court of Justice, as the chief judicial organ of the United Nations, in “contentious disputes” between States, is subject to the principle of consent. It can obtain jurisdiction in three ways. Learn more about the International Court of Justice roles here.

Historical Developments of Sources of Law and Law Making Institutions from the XII Tables to the Corpus Juris Civilis (CJC): Sources of Law

See the entries about: From the XII Tables to the Classical Period of Roman Law, andthe entry about: Post-Classical Period to the Corpus Juris Civilis (3rd to 6 th Century)

Sources of Law in International Economic Law

In international economic law, sources of law includes the following legal areas, with coverage in this world legal encyclopedia:

    li> General Principles of Law in International Economic Law
  • Customary International Law in International Economic Law
  • Role of Courts in International Economic Law
  • Treaties and Treaty Interpretation in International Economic Law
  • Soft Law in International Economic Law
  • Networking and Informal Cooperation in International Economic Law
  • Role of Empirical Research in International Economic Law


See Also

  • Civil Code History
  • Codification History
  • Historical Developments
  • Sources Of Law
  • Law Making Institutions


See Also

  • Legal theory
  • Jurisprudence
  • Theory of Law
  • Philosophy of Law


See Also

  • Legal Biography
  • Legal Traditions
  • Historical Laws
  • History of Law

Further Reading