The purpose of the third edition of An Introduction to Contemporary International Law: A Policy-Oriented Perspective is to propose to readers an answer to the question: What is international law? The answer given follows in the tradition of the New Haven School, whose policy-science approach to international law has its origins in the works of Professors Myres S. McDougal and Harold D. Lasswell of Yale Law School. Beginning in the mid-twentieth century, Professors McDougal and Lasswell and their collaborators sought to understand and to describe the forces rapidly reshaping the global landscape after the end of World War II. According to them, international law is not static but is a process by which members of the world community attempt to clarify and secure their common interests through authoritative decisions and controlling practices. For students wishing to understand international law, I submit that there is no better place to start than with the New Haven School’s systematic approach to world events and its accompanying set of intellectual tools for identifying and describing the factors that underlie international legal order.