Custom, Principles & Teachings in International Law

Updated March 31, 2011.
Prepared by Jonathan Franklin; updated by Lori Fossum (2011).

This guide defines and identifies sources for custom, principles, and teachings in international law.

LexisNexis and Westlaw are restricted to users with individual IDs or passwords. HeinOnline is UW restricted.

Customary International Law

"Customary international law is the generalization of the practice of States" Fisheries Case, ICJ Reports (1951) 191.

For example, United Nations General Assembly resolutions can often form the basis for an argument based on custom. For additional discussion on how to find UN resolutions, see the United Nations Research guide.

For additional information about customary law, see Ralph F. Gaebler, "Conducting Research in Customary International Law," in Contemporary Practice of Public International Law. KZ1234 C66 1997 at Classified Stacks



"Principles of Law Recognized by Civilized Nations" means principles that virtually all industrialized nations adhere to. They can be substantive or procedural principles, such as equitable claims that appear in both the common and civil law systems.

Principles are found by completing a comparative law study of how a particular issue is dealt with in a wide range of jurisdictions.

For additional information, see the Gallagher guide on Foreign Law Research.



"Teachings of the Most Highly Qualified" means scholarly writings by leading minds regarding how to treat a particular topic or question.

Teachings can be found in secondary sources (treatises, yearbooks, journals). Use the periodical indexes and library catalog.

Consult annotated bibliographies and research guides, such as Germain's Transnational Law Research. K85.G47 1991 at Reference Office

Several specific sources of teachings are:

  • Yearbook of the International Law Commission. KZ1287.U55Y43 at Classified Stacks
  • International Law Commission website
  • Encyclopedia of Public International Law. KZ1160.E53 1992 at Classified Stacks


U.S. Perspective

For the U.S. perspective on customs, principles, and teachings, consult the following sources.

Restatement of the Law, Third, the Foreign Relations Law of the United States. KF395.F67 1987 at Reference Area. Available on LexisNexis & Westlaw: REST-FOREL

The U.S. State Department's Office of the Legal Adviser publishes digests to provide the views and practices of the United States in public and private international law.

  • Digest of United States Practice in International Law, 1973-date. KZ237.7.D544 at Classified Stacks. Online beginning with 1989.
  • Prior to 1973, Digest of International Law. KZ237.7.W45 at Classified Stacks
  • The Digest is updated quarterly in the American Journal of International Law (at Compact Stacks), under the section titled "Contemporary Practice of the United States Relating to International Law." Available on HeinOnline (UW Restricted), LexisNexis & Westlaw: AMJIL
  • Cumulative Digest of United States Practice in International Law, 1981-88. KZ237.7.D544 at Classified Stacks
  • West's Federal Practice Digest 4th. KF127.W484 at Reference Area
  • West's Federal Practice Digest 3d, 1975-beginning of 4th. KF127.W483 at Reference Area
  • Foreign Relations of the United States is the official record of the foreign policy of the United States and includes numerous declassified documents from various federal agencies. KZ233.F67 at Classified Stacks


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