The International Court of Justice at The Hague is the principal judicial organ of the UN, and the successor of the Permanent Court of International Justice (1923-1946), which was the first real permanent court of justice at the international level. This book analyses the ground-breaking contribution of the Permanent Court to international law, both in terms of judicial technique and the development of legal principle. The book draws on hitherto unpublished archival material left by judges and other persons involved in the work of the Permanent Court, giving fascinating insights into many of its most important decisions and the individuals who made them (Huber, Anzilotti, Moore, Hammerskjöld and others). At the same time it examines international legal argument in the Permanent Court, basing its approach on a developed model of international legal argument that stresses the intimate relationships between international and national lawyers and between international and national law.