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Sources of Public International Law

This guide will help you locate the sources necessary for researching a problem involving public international law.

Books

Given the complexity involved when working with custom it may be helpful to start with a book that offers a deeper understanding of the theory behind its creation and operation:

Introduction

Establishing customary international law always requires demonstration of two essential elements: 1) objective, evidence of a general and consistent state practice, and 2) subjective, opinio juris, evidence of a state's understanding of their legal obligation.

In 1951, the I.L.C. issued the report Ways and Means for Making the Evidence of Customary International Law More Readily Available. This report lists the following sources as evidence of customary international law: 

1) Treaties; 
2)  Decisions of National Courts and International Tribunals;  
3)  National Legislation; 
4)  Diplomatic Correspondence;
5)  Opinions of National Legal Advisors; and 
6)  The Practice of International Organizations. 

Since some of the sources are covered elsewhere in this guide, this tab will focus on sources 4, 5, and 6.
 

Diplomatic Correspondence & Opinions of National Legal Advisors

The Foreign Relations of the United States series presents the official documentary historical record of major foreign policy decisions and significant diplomatic activity of the U.S. Government as compiled by the Office of the Historian.

The Department of State Office of the Legal Advisor publishes the Digest of United States Practice in International Law to provide a historical record of the views and practice of the government in public and private international law over a period of time. The editors cite, excerpt or reprint documents from the State department and other agencies and departments. 

For other countries or geographic regions, you can try searching our catalog for the name of the place and year book (or yearbook) or have a look at Hein's collection online arranged alphabetically:

The Practice of International Organizations

The United Nations General Assembly is a good place to start when looking for evidence of state practice and obligation because most states are represented there.  Looking for their resolutions is an efficient way to go and the U.N. makes it very easy to track them down:

You may have similar luck with other organizations but keep in mind their structure and how and which countries participate.  Here is a link to track down their websites: