This fully revised, classic treatise explores the historical evolution and contemporary intricacies of international law. Still incisive and irreverent, it remains a readable and yet nuanced text for a variety of audiences, including university and law school students, practitioners, researchers, and others who want to know what international law is and what it does in the twenty-first century. The fourth edition features new authorship and weaves in-depth considerations of key cases, core disputes, and essential international agreements into a broad overview of all important aspects of the subject. Readers will find an authoritative discussion of traditional topics such as the sources of international law and the methods of international dispute resolution alongside cutting-edge issues such as cyberwarfare, global migration, climate change, and the evolving law of jurisdiction and immunities in domestic courts.