This book explores the scope and limits of what is appropriate for regional action in the maintenance of peace and security. It offers a comparative study of legal regulation of the use of force in the maintenance of peace and security of different security regions in the context of the UN system and general international law. The book examines the post-Cold War legal documents and practice of the regional organizations of six security regions of the world (Africa, Asia, the Americas, the Middle East, the Russian sphere of influence and the Euro-Atlantic region), and in doing so offers a unique international and comparative perspective towards regional characteristics that may influence the possibility for coherent action in a UN context. Dace Winther explores the controversial topics of regional humanitarian intervention and robust regional peacekeeping without a UN mandate, what is regarded as appropriate for regional action in different security regions of the world, and if the approaches of the regions differ, what factors could have an influence. The book is highly relevant in a global climate where regional mechanisms take an ever more active part in the maintenance of international peace and security, including the use of force. The book will be of great interest to students and academics of International Law, International Relations and Security Studies.