Customary international law

Customary international law is an aspect of international law involving the principle of 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.

Many governments accept in principle the existence of customary international law, although there are differing opinions as to what rules are contained in it. A rule becomes customary international if two requirements are met: (1) There is a state practice that "appears to be sufficiently widespread, representative as well as consistent" showing that a significant number of states have used and relied on the rule in question and the concept has not been rejected by a significant number of states,^[1]^[2] (2) states were motivated by a belief that they were legally compelled to accept the legitimacy of the rule in question because customary international law obligated them to do so (opinio juris).^[1]

In 1950, the International Law Commission listed the following sources as forms of evidence of customary international law: treaties, decisions of national and international courts, national legislation, opinions of national legal advisors, diplomatic correspondence, and practice of international organizations.^[3]^[4] In 2018, the Commission adopted Conclusions on Identification of Customary International Law with commentaries.^[5] The United Nations General Assembly welcomed the Conclusions and encouraged their widest possible dissemination.^[6]

^ ^a ^b Wood, Michael C. (2014-05-22). "Second report on identification of customary international law by Michael Wood, Special Rapporteur". UN. Retrieved 2023-12-13.
^ "Customary International Law – International Law". USLegal. Retrieved 2023-12-11.
^ See Evidence of State practice Archived 2008-12-26 at the Wayback Machine.
^ Merkouris, Panos (2022), Kammerhofer, Jörg; Arajärvi, Noora; Merkouris, Panos (eds.), "Interpreting Customary International Law: You'll Never Walk Alone", The Theory, Practice, and Interpretation of Customary International Law, Cambridge University Press, pp. 347–369, doi:10.1017/9781009025416.017, ISBN 978-1-316-51689-8
^ Report of the International Law Commission. Seventieth session (30 April-1 June and 2 July-10 August 2018). A/73/10. New York: United Nations. 2018. pp. 12–116.
^ Resolution adopted by the General Assembly. Identification of customary international law. A/RES/73/203. United Nations. 2018-12-20. Retrieved 2020-01-27.

[Wood_Law_2014_h359-1] Wood, Michael C. (2014-05-22). "Second report on identification of customary international law by Michael Wood, Special Rapporteur". UN. Retrieved 2023-12-13.

[Legal_g698-2] "Customary International Law – International Law". USLegal. Retrieved 2023-12-11.

[3] See Evidence of State practice Archived 2008-12-26 at the Wayback Machine.

[4] Merkouris, Panos (2022), Kammerhofer, Jörg; Arajärvi, Noora; Merkouris, Panos (eds.), "Interpreting Customary International Law: You'll Never Walk Alone", The Theory, Practice, and Interpretation of Customary International Law, Cambridge University Press, pp. 347–369, doi:10.1017/9781009025416.017, ISBN 978-1-316-51689-8

[5] Report of the International Law Commission. Seventieth session (30 April-1 June and 2 July-10 August 2018). A/73/10. New York: United Nations. 2018. pp. 12–116.

[6] Resolution adopted by the General Assembly. Identification of customary international law. A/RES/73/203. United Nations. 2018-12-20. Retrieved 2020-01-27.

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