Focusing on East Asia, this collection explores the paradox of functional regional cooperation in the areas of humanitarian assistance, disaster relief, and UN Peacekeeping operations, in a context of increasing regional tensions and threats. East Asia - comprising the states of the Association of Southeast Asian Nations and China, Japan, the Republic of Korea and the Democratic People's Republic of Korea - is facing a range of human, traditional, climate and ideational threats. In addressing some of these threats particularly those arising from climate induced disasters this region has been able to develop some ad-hoc cooperative practices that, according to functional logics of regional integration, could lead to longer term sustained coordinated responses and even regional partnerships. Similarly, the region is increasingly contributing to UN peacekeeping operations where these states also cooperate in the context of an UN-led mission. Yet, despite the potential for these interactions to lead to greater regional integration and coordinated action in responding to a range of security threats, these interactions are increasingly taking place in a context of animosity both between regional powers and with extra-regional powers. This edited collection explores these functional interactions and posits conclusions about the potential for longer term sustained coordinated action. These papers engage with a range of theoretical approaches in explaining the patterns of relations that are present in the region in relation to humanitarian assistance, disaster relief, and UN peacekeeping operations. The chapters in this book were originally published as a special issue of the Australian Journal of International Affairs.