This book concentrates on one of the major concerns of the United Nations: world peace. Aiming to trace the development of the concept of peace from the foundation of the UN until today, the book investigates on what conceptual understanding the UN was instituted in 1945 and what notion of peace has become apparent in subsequent UN policy as it is performed by the primary UN organs. Along the lines of this research program, the book seeks to reveal the changing underlying assumptions about how a peaceful world order looks and how it should be brought about. Beyond these aspects of semantic change, the book also explores the institutional dimension of this organizational concept by carving out how it is anchored in functional-normative structures of the world organization, its policy, and rhetoric. It builds on an interdisciplinary approach of institutional analysis and conceptual explanation that combines interpretive methods from international law scholarship, conceptual history and policy analysis.