Introduction: What is international law and why does it matter for international relations?

This introductory chapter provides an overview and a brief history of international law. Why should students of international relations be interested in international law? International politics and international law are so closely intertwined that one cannot be understood without understanding the other. The United Nations describes international law as ‘the legal responsibilities of States in their conduct with each other, and their treatment of individuals within State boundaries’. Just as domestic law frames a political community and regulates relations among its members, international law helps to frame international society, to signal its core values, and to regulate relations among states and other actors. The chapter then considers two philosophical traditions that have shaped the study and practice of international law over the past four centuries: natural law and legal positivism.