International Law (4th edition)
by Jan Klabbers · Cambridge University Press
The best readable single-volume introduction to the logic of the field. A single-author textbook of about 410 pages covering sources, treaties, statehood, jurisdiction, state responsibility, the UN, the use of force, human rights and dispute settlement. It explains why the system works as it does, not only what the rules are.
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More resources on International Law
The Internationalists: How a Radical Plan to Outlaw War Remade the World
Covers the 'how enforcement actually works' part of the topic note better than any textbook, in accessible prose. A history of the 1928 Peace Pact that outlawed war and how it reshaped the international legal order. It argues that international law is enforced mainly through 'outcasting', meaning exclusion and sanctions, not through a world police.
Brownlie's Principles of Public International Law (9th edition)
The standard one-volume doctrinal treatise on public international law, cited by courts and practitioners. It covers sources, statehood, territory, the law of the sea, jurisdiction, immunities, state responsibility, human rights and dispute settlement.
How Does Law Protect in War? (ICRC Online Casebook)
ICRC's online casebook on international humanitarian law: a 15-chapter outline of the law, more than 450 case studies and documents with discussion questions, and model course outlines, written by Marco Sassòli and co-authors. Practice-based cases show how the rules apply in real conflicts.
International Humanitarian Law in Theory and Practice
Six-module Leiden University course on the law of armed conflict: conflict classification, conduct of hostilities, protection of persons, and implementation and enforcement, taught through a running case scenario and interviews with ICRC and US Naval War College experts.
International Law in Action: A Guide to the International Courts and Tribunals in The Hague
The best structured, accessible entry point on how international courts actually operate and how far their jurisdiction depends on state consent. Leiden University course on international dispute settlement, covering the International Court of Justice, arbitration and international criminal courts through selected cases and interviews with judges and lawyers, with themes of state consent and law versus politics.
UN Audiovisual Library of International Law: Lecture Series
A permanent UN Office of Legal Affairs collection of recorded lectures by leading judges, scholars and practitioners across roughly 38 subject areas, including treaties, the UN system, courts and tribunals, human rights and armed conflict, with outlines and readings. Primary-source, free, and covers every branch the topic note lists; each lecture is by a top authority in that subfield, so it works as a modular reference course.