'No-one is better at explaining the nuance of international law while keeping an eye squarely on the details than Jan Klabbers. This new edition of his groundbreaking textbook is a terrific update to an essential book. The book charts the theories and assumptions that make up the international legal system while telling engaging stories about the histories and cases that constitute its practice. The combination is readable, informative, and unmatched among international law textbooks.' Ian Hurd, Professor of Political Science and Director of the Weinberg College Center for International and Area Studies, Northwestern University