Skip to Main Content

Public International Law: A Beginner's Guide

This guide, from the Law Library of Congress, provides resources for public international law, including treaties, customary international law, principles of international law, writings of publicists, and judicial decisions.


In an 1860 textbook, Introduction to the Study of International Law, Theodore Woolsey began his definition of international law by stating, "[n]ations or organized communities of men differ from the individual men of a state, in that they are self-governed, that no law is imposed on them by an external human power, but they retain the moral accountable nature, which lies at the foundation of a single society." Over 150 years later, these concepts addressed by Woolsey have evolved and become more explicit, growing into a set of doctrines, rules, and norms known as public international law.

Detroit Publishing Company, publisher. The Globe, Swanage, England. Between ca. 1890 and ca. 1900. Library of Congress Prints and Photographs Division.

Public international law is the body of law created through the interactions between nations, or as the Restatement of the Law, Third: Foreign Relations Law of the United States (Restatement Third) explains, "International law is the law of the international community of states. It deals with the conduct of nation-states and their relations with other states, and to some extent also with their relations with individuals, business organizations, and other legal entities." Nations adhere to the concepts of international law through treaties, custom, and interpretations by both their own domestic judiciaries and international tribunals.

Public international law does not have a conventional enforcement framework, so no worldwide policing organization exists to ensure that treaties are followed. Instead, nations subject themselves to international law by adhering to treaties, and by accepting customary laws and agreed-upon general principles of law. Mutual respect among nations and the understanding that a breach in any concept could lead to retaliation from other nations, through economic or even military sanctions, generally causes nations to follow the accepted standards of public international law.

This research guide focuses on how public international law is derived, how it evolves, and how it can be researched. Researching this topic often involves reliance on a broad spectrum of different resources, ranging from explicitly written multi-lateral treaties, to interpretations of internationally accepted legal principles described by scholars.

Below you will find a list of selected legal reference materials relating to public international law from the Law Library's collection.

The following titles link to fuller bibliographic information in the Library of Congress Online Catalog. Links to additional digital content are provided when available.