This article examines regional environmental governance (REG) through the lens of human geography theory on scale. Drawing on a case study of the Micronesia Challenge, a regional conservation commitment among five Pacific islands, I advance a critical theory of REG as a scaling process and tool of politics through which regions are (re)made and mobilized in support of diverse agendas. Results highlight understudied dimensions of REG, including: motivations for scaling environmental governance to regions, the co-production of regional and global environmental governance, the mutable expression of regionality within REG, and the ways in which REG is leveraged for resource mobilization, global visibility and influence, and conservation. The potential for REG to empower subaltern groups while advancing conservation is promising, and an important area for future research. The overall contribution of this article is a more complex, politicized understanding of REG that complicates a scholarly search for its inh...