Environmental degradation in Southeast Asia has been implicated in what some describe as a failure of regional cooperation and a crisis of regional identity and credibility within ASEAN. This article examines environmental decline in Southeast Asia as a consequence of the region's changing political economy and modes of production and suggests that regional cooperation on environmental challenges is more likely to be successful if it reflects some form of bounded cosmopolitanism embedded in a regional community of rights and duties. Drawing on identity-based accounts of regional cooperation to explore the relationship between ideas, interests and policy in the region, it identifies three phases of environmental cooperation since 1977. It argues that, despite apparent ideational and institutional advances over this period, ASEAN has been unable to respond effectively to regional environmental challenges for normative as well as material reasons. Yet while environmental cooperation has been constrained by the ASEAN way, the imperatives for such cooperation have challenged the ASEAN's political norms and confirmed the ambiguities of regional identity within Southeast Asia.