Peace operations are the UN´s flagship activity. Over the past decade, UN blue helmets have been dispatched to ever more challenging environments from the Congo to Timor to perform an expanding set of tasks. From protecting civilians in the midst of violent conflict to rebuilding state institutions after war, a new range of tasks has transformed the business of the blue helmets into an inherently knowledge-based venture. But all too often, the UN blue helmets,policemen, and other civilian officials have been "flying blind" in their efforts to stabilize countries ravaged by war. The UN realized the need to put knowledge, guidance and doctrine, and reflection on failures and successes at the center of the institution. Building on an innovative multi-disciplinaryframework, this study provides a first comprehensive account of learning in peacekeeping. Covering the crucial past decade of expansion in peace operations, it zooms into a dozen cases of attempted learning across four crucial domains: police assistance, judicial reform, reintegration of former combatants, and mission integration. Throughout the different cases, the study analyzes the role of key variables as enablers and stumbling blocks for learning: bureaucratic politics, the learninginfrastructure, leadership as well as power and interests of member states. Building on five years of research and access to key documents and decision-makers, the book presents a vivid portrait of an international bureaucracy struggling to turn itself into a learning organization. Aimed at policy-makers,diplomats, and a wide academic audience (including those working in international relations, peace research, political science, public administration, and organizational sociology), the book is an indispensable resource for anyone interested in the evolution of modern peace operations.