This article illuminates the value of the concept of the region in political ecology and environmental justice studies by presenting three arguments about the role of regions in environmental justice social movements engaged in climate change mitigation in California's San Joaquin Valley. First, regional planning agencies and environmental justice advocates are engaged in conflicts over not only the content of regional climate change plans, but the very definitions of region and the authority used to put these regional visions into action. Second, regional organizing provides environmental justice movements with new opportunities to address regional economic patterns and to negotiate with regional planning agencies, both of which influence local manifestations of environmental injustice. Third, regional strategies raise significant dilemmas for these movements as they try to sustain engagement across extensive spatial territories and engage with a broad set of policy and economic protagonists. Together, this analysis demonstrates that a dynamic approach to regions, regionalism, and regionalization can assist political ecology and environmental justice scholars in their common aim of understanding the co-production of social and environmental inequity and collective action to change it.