The new contributions in this book, by acknowledged leaders in the field, examine the delivery of effective aid under fire, and securing the peace in environments where governance is fragile. They bridge the cultural divide between the security and development professions at a time of unprecedented global economic integration, geopolitical turbulence, and novel threats to international peace and security.More than a billion people live in countries where governance is weak, poverty is rampant, and economies are depressed. Failed and frail states provide ideal breeding grounds for civil strife, criminality, and "new wars" that target civilians, use children as combatants, and commit massive human rights violations. The new security risks loom within national borders, while the capacity of the international community to intervene ‘behind borders’ remains inadequate. Policy making for security still relies heavily on military responses. Yet military responses cannot address, and may even worsen, the social and cultural antecedents of civil strife and social resentment. Similarly, development aid policy and practice are poorly adapted to the new realities of frail governance and insecure operating environments in aid recipient countries.This book was previously published as a special issue of the leading journal Conflict, Security and Development.