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Customary international law


Customary international law

Customary international law are those aspects of international law that derive from custom. Along with general principles of law and treaties, custom is considered by the International Court of Justice, jurists, the United Nations, and its member states to be among the primary sources of international law.

The vast majority of the world's governments accept in principle the existence of customary international law, although there are many differing opinions as to what rules are contained in it.


  • Recognition of customary international law 1
    • Jus cogens 1.1
  • Codification of international customary law 2
    • Silence as consent 2.1
  • The International Court of Justice 3
  • Bilateral versus multilateral customary international law 4
  • Other customary international laws 5
  • See also 6
  • References 7
  • Bibliography 8
  • External links 9

Recognition of customary international law

The International Court of Justice Statute defines customary international law in Article 38(1)(b) as "evidence of a general practice accepted as law."[1] This is generally determined through two factors: the general practice of states and what states have accepted as law.[2]

There are several different kinds of customary international laws recognized by states. Some customary international laws rise to the level of jus cogens through acceptance by the international community as non-derogable rights, while other customary international law may simply be followed by a small group of states. States are typically bound by customary international law regardless of whether the states have codified these laws domestically or through treaties.

Jus cogens

See jus cogens.

A peremptory norm (also called jus cogens, Latin for "compelling law") is a fundamental principle of international law which is accepted by the international community of states as a norm from which no derogation is ever permitted. These norms rooted from Natural Law principles,[3] and any laws conflicting with it should be considered null and void.[4] Examples include various international crimes; a state which carries out or permits slavery, torture, genocide, war of aggression, or crimes against humanity is always violating customary international law.[5]

Jus cogens and customary international law are not interchangeable. All jus cogens are customary international law through their adoption by states, but not all customary international laws rise to the level of peremptory norms. States can deviate from customary international law by enacting treaties and conflicting laws, but jus cogens are non-derogable.

Codification of international customary law

Some international customary laws have been codified through treaties and domestic laws, while others are recognized only as customary law.

The laws of war, also known as jus in bello, were long a matter of customary law before they were codified in the Hague Conventions of 1899 and 1907, Geneva Conventions, and other treaties. However, these conventions do not purport to govern all legal matters that may arise during war. Instead, Article 1(2) of Additional Protocol I dictates that customary international law governs legal matters concerning armed conflict not covered by other agreements.[6][7]

Silence as consent

Generally, sovereign nations must consent in order to be bound by a particular treaty or legal norm. However, international customary laws are norms that have become pervasive enough internationally that countries need not consent in order to be bound. In these cases, all that is needed is that the state has not objected to the law. However, states that object to customary international law before these laws may not be bound by them unless these laws are deemed to be jus cogens.[8]

The International Court of Justice

The Statute of the International Court of Justice acknowledges the existence of customary international law in Article 38(1)(b), incorporated into the United Nations Charter by Article 92: "The Court, whose function is to decide in accordance with international law such disputes as are submitted to it, shall custom, as evidence of a general practice accepted as law."

Customary international law "... consists of rules of law derived from the consistent conduct of States acting out of the belief that the law required them to act that way."[9] It follows that customary international law can be discerned by a "widespread repetition by States of similar international acts over time (State practice); Acts must occur out of sense of obligation (opinio juris); Acts must be taken by a significant number of States and not be rejected by a significant number of States."[10] A marker of customary international law is consensus among states exhibited both by widespread conduct and a discernible sense of obligation.

The International Court of Justice held in Nicaragua v. United States that the elements of an international customary law would be opinio juris (belief that an action was carried out by states due to a legal obligation) which is then proven by existing state practices.[11]

Bilateral versus multilateral customary international law

The recognition of different customary laws can range from simple bilateral recognition of customary laws to world-wide multilateral recognition. Regional customs can become customary international law in their respective regions, but do not become customary international law for nations outside the region. The existence of bilateral customary law was recognized by the International Court of Justice in the Right of Passage Over Indian Territory case between Portugal and India, in which the court found "no reason why long continued practice between the two states accepted by them as regulating their relations should not form the basis of mutual rights and obligations between the two states."[12]

Other customary international laws

Other examples accepted or claimed as customary international law include the principle of non-refoulement and immunity of visiting foreign heads of state. United Nations Security Council in 1993 adopted Geneva conventions as customary international law because since the time being it has transformed itself into customary international law. If any treaty or law has been called as customary international law then parties which has not ratified treaty will be bound to observe its provisions in good faith.[13]

See also


  1. ^ "Statute of the International Court of Justice". Retrieved 30 May 2012. 
  2. ^ Yoram Dinstein. 2004. The Conduct of Hostilities under the Law of International Armed Conflict, pp. 5. Cambridge: Cambridge University Press.
  3. ^ Władysław Czapliński. Jus Cogens and the Law of Treaties. In C.Tomuschat and J.M. Thouvenin (eds). 2006. The Fundamental Rules of the International Legal Order, pp. 83-98. Netherlands: Koninklijke Brill NV
  4. ^ Article 53 of the Vienna Conventions on the Law of Treaties (1969)
  5. ^ M. Cherif Bassiouni.1998. International Crimes: jus cogens and Obligatio Erga Omnes, Law & Contemporary Problems, 59: 63-74
  6. ^ "Protocol Additional to the Geneva Conventions of 12 August 1949, and Relating to the Protection of Victims of International Armed Conflicts (Protocol I)". 8 June 1977. Retrieved 30 May 2012. 
  7. ^ Yoram Dinstein. 2004. The Conduct of Hostilities under the Law of International Armed Conflict, pp. 6-7. Cambridge: Cambridge University Press.
  8. ^ Fisheries Case (United Kingdom v Norway) (Judgement) [1951] ICJ Rep 116, 131 where it is stated '…the ten-mile rule would appear to be inapplicable as against Norway inasmuch as she has always opposed any attempt to apply it to the Norwegian coast.' The case can be found at:
  9. ^ Rosenne, Practice and Methods of International Law, p. 55.
  10. ^ "Customary International Law". 
  11. ^ Malcolm Shaw. 2008. International Law (Sixth Edition). New York: Cambridge University Press, pp. 72-93
  12. ^ "Right of Passage over Indian Territory (Merits) (Port. v. India), 1960 I.C.J. 6 (Apr. 12)". 
  13. ^ Certain Norwegian Loans (France v Norway) (Jurisdiction) [1957] ICJ Rep 9, 53.


  • Customary International Law, Max Planck Encyclopedia of Public International Law
  • Customary international humanitarian law International Committee of the Red Cross
  • A Brief Primer on International Law With cases and commentary. Nathaniel Burney, 2007.
  • Customary International Law - Bibliographies on the topics of the International Law Commission (no.13 in the list) (UNOG Library)

External links

  • Customary IHL Database
  • Peace Palace Library - Research Guide
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