Hans Kelsen's efforts in the areas of legal philosophy and legal theory are considered by many scholars of law to be the most influential thinking of this century. This volume makes available some of the best work extant on Kelsen's theory, including papers newly translated into English. The book covers such topics as competing philosophical positions on the nature of law, legal validity, legal powers, and the unity of municipal and international law. It also throws much light on Kelsen's intellectual milieu--as well as his intellectual debts.