Customary International Law, General Principles of Law, and Other Sources

Research Guides & Background Information

Background Information

Department of State

Research Guides & Background Information


Domestic Law Concerning a Country's International Obligations

Resolutions, Declarations, and Legislative Acts of Intergovernmental

IGO yearbooks


Judicial Decisions of
International Tribunals

Court Decisions of Individual Countries Concerning International Obligations

Scholarly Works

Review Questions

State Practice: Research Guides & Background Information

Sources of State Practice in International Law (Ralph Gaebler and Maria Smolka-Day, eds., 2002-) is one of the best places to start researching the practice of other countries. It outlines the sources that provide evidence of state practice for about 15 countries.

Researching Public International Law provides guidance for finding the state practice of other countries (click on “Custom and State Practice”).

The National Treaty Law and Practice series published by the American Society of International Law includes volumes that cover about 15 countries.

To find materials on the state practice of individual countries, search library catalogs with the subject heading international law [country].

Research Tip
Compiled state papers or diplomatic archives are among the best sources of evidence for the rules of customary international law, to find them, search library catalogs with the subject headings: [country]--foreign relations and [country]--history--sources.


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