Most studies of regionalism in Southeast Asia pay little attention to environmental concerns as part of the region's empirical dynamic. In contrast, this article examines the ways in which governments have come to "govern" environmental issues at a regional scale under the auspices of ASEAN, against the backdrop of debates about the political topography of Southeast Asian regionalism. The framework adopted here brings together analyses of the public space of formal regional governance arrangements, the inter-subjective space of regional identity building, and the private space of regional social practices. Underpinning this is the question of whether moves to supposedly "flatter" forms of regional governance have been accompanied by for more democratic or participatory forms of regionalism. I conclude that regional environmental structures under ASEAN are more akin to "invited spaces" and have generally failed to offer effective channels of communication for, or democratic representation of, a wider range of stakeholders, including civil society groups and local communities.