I. General Background on Customary International Law


Crawford, Part I Preliminary Topicsin  The Sources of International Law, Brownlie’s Principles of Public International Law (8th Ed., Oxford Public International Law, 2012) [unavailable online without purchase]

  • Details the sources of international law – treaties, custom, general principles, judicial decisions, and subsidiary sources. Explains the elements of custom and reviews foundational cases.

Schlutter, Developments in Customary International Law (2010) [unavailable online without purchase]

  • Provides an overview of the current status of customary international law. Includes a comprehensive synopsis of the current literature and contrasts the practice of the ICTY/ICTR with jurisprudence of the International Court of Justice.

Mendelson, The Formation of Customary International Law (1998) [available online with subscription]

  • Detailed overview of customary international law elements and identification. Explores the creation of new principles of customary international law. Details the benefits and challenges in utilizing customary international law.


Meron, Revival of Customary Humanitarian Law, Am.J.Int’l.L (2005) [available online with subscription]

  • The author asserts that at least in the field of humanitarian law, customary law continues to thrive and to depend in significant measure on the traditional assessment of both state practice and opinio juris. In particular, this essay explores the ways that the nullum crimen sine lege principle has affected the application of customary humanitarian law by the criminal tribunals. 

Mettraux, Crimes Against Humanity in the Jurisprudence of the ICTY and ICTR, Harv Int’l L.J. (2002)[available online with subscription]

  • This article analyzes how the International Criminal Tribunal for the former Yugoslavia (ICTY) and the International Criminal Tribunal for Rwanda (ICTR) have played a crucial role in the transformation of crimes against humanity into an international offense.

Scharf, Accelerated Formation of Customary International Law, ILSA J. of Int. & Comparative Law (2014) [available for free online]

  • This article examines the phenomenon of accelerated formation of customary international law. It argues that in periods of fundamental change, whether by technological advances, the commission of new forms of crimes against humanity, or the development of new means of warfare or terrorism, customary international law may form much more rapidly and with less state practice than is normally the case to keep up with the pace of developments.


International Court of Justice, North Sea Continental Shelf Cases (1969) [available for free online]

  • The foundational International Court of Justice decision which lays out customary international law’s dual requirements of state practice and opinio juris. Highlights the issue of “specially affected” states and dispels the notion that duration of practice is a necessary element of customary international law.