Originally published in 1958, this book assesses the continuity and variety of international societies as they have existed in recent history. Although the study of international institutions is firmly based on a foundation of law, this book also encompasses sociology, history and politics. The introduction defines the elements of international society in terms of the accepted principles of group psychology. Part 1 considers the origins of 20^th Century international institutions. This historical analysis runs from the ancient civilizations through to the greatly changed relations which followed World War II. The general notions and sources of international law are then examined. Part 2 deals with the structure of day-to-day relations between States and the means of recognizing changes within a State. The United Nations and principal regional organizations are also examined.