In the wake of the calamitous events of September 11, 2001, public international law has endured some of the greatest tests of its history and emerged as one of the most resilient and potent tools available to human society in facing the unsettling global conditions of the early twenty-first century. The second edition of Public International Law provides a systematic introduction to the international legal system, including its key structural and institutional aspects as well as its core substantive topics. Analysis of all topics has been extensively revised and expanded since the first edition in order to reflect the many legal changes that have occurred since 2001. Several new discussions have also been introduced, considerably expanding the substantive coverage of the text. In particular, given the centrality of the topic to the functioning of the modern international legal system, an entirely new chapter on the use of force in international relations has been added.