Book excerpt: One of the most challenging environmental threats to the ten countries of the Association of Southeast Asian Nations (ASEAN) has been the haze, the sickening and deadly cloud of smoky pollution caused by widespread burning of land and forests in Indonesia. This book examines both the threat and response to it by analysing environmental cooperation in Southeast Asia from an international regime perspective. Tracing the development of regional cooperation on the haze and evaluating the effectiveness of the cooperation, the author argues that the haze crisis, combined with the economic crisis of 1997, has profoundly challenged the ASEAN modus operandi, and resulted in ASEAN’s efforts to establish an environmental regime to cope with environmental challenges. The emerging ASEAN haze regime is a unique case study of a regional environmental institution in multi-levelled global environmental governance. Based on in-depth original research, this case study is integrated into international relations, political science, and comparative political analysis literatures and contributes to a better understanding of processes within the regional organisation.