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Sources of Public International Law

The sources of international law to be used in US courts are set out in the Restatement (3d) of the Foreign Relations Law of the United States. The sources for most international courts are set out in the Statute of the ICJ. This guide helps you find them


A useful print resource to use to find state practice is:

For assistance in researching the law of particular jurisdictions, see the Library of Congress Guide to Law Online -  see Nations of the World

  • A helpful guide for researching Customary International Law is Silke Sahl's Guide (updated to 2016)
  • To assist you to find, verify and research multinational and foreign law treaties and international agreements in the UCONN Law Library, see UCONN Law LibGuide
  • See also the Research Guides listed at the Home tab of this guide.



Customary International Law

As the Restatement says: "Customary international law results from a general and consistent practice of states followed by them from a sense of legal obligation."

Customary international law may be found articulated in multilateral and bilateral treaties; actions taken by States through international organizations (e.g. resolutions of the U.N. General Assembly); decisions of international tribunals; domestic court decisions and national domestic legislation; diplomatic correspondence and administrative decisions. The age of the material you are looking for will, in many cases, determine whether or not you can find it online.

Look at the resources the UCONN Law Library has listed below to find these sources of Customary International Law.




Digests & Year Books

For information on the the state practice of international law, look for country specific digests and international law year books (sometimes spelled yearbook)

For instance, the UCONN Law Library has the following (selected):

  • Australia - Australian Year Book of International Law  electronic.
  • Japan - Japanese Yearbook of International Law print
  • Netherlands - Netherlands Yearbook of International Law  print
  • Poland - Polish Yearbook of International Law  electronic

Law Library does not have complete holdings of many of these titles in print. Most of the electronic editions are on HeinOnline (Net Id may be required).

Websites & Databases


  • A helpful website for finding by jurisdiction many of the materials needed for determining customary international law online is Worldlii
  • Use the UCONN Law Library Research Database Foreign Law Guide to find non-U.S. primary legal sources--legislation, case law and executive documents-- online and in print, official and unofficial, including English translations, if available.
  • Another helpful website for locating electronic format primary source material is the American Society of International Law’s EISIL

Find international actions taken through organizations at those organizations' websites.

For instance:

  • Council of Europe - For instance, click on Human Rights to see what COE is doing in this area.

Also look at NGO and international organization sites for databases of laws  and conventions regarding particular topics.

For instance:

  • Refworld - database of refugee laws and jurisprudence a the UNHCR -United Nations Refugee Agency





Books & Articles

To find books on Customary International Law in library catalogs, including UCONN Law Library's online catalog, use the LC Subject Heading: Customary Law, International

Here are selected recent books - dealing more with the theory rather than the rules of Customary International law - in the UCONN Law Library:


To find books on the topic that the UCONN Law Library does not hold, use WorldCat (NetID required)

Use the LC Subject Heading: Customary Law, International to find relevant articles in periodical indexes and UCONN Law Library's research databases [NetID may be required] such as, Hein Online and JSTOR.