In many areas experiencing severe impacts from climate change, it is not the state, but rather rebel groups who wield authority over populations. Rebels are often engaged in responding and adapting to the risks and impacts of climate change as part of their local governance efforts; however, a systematic consideration of the activities and implications has been lacking. This Element looks at a set of behaviors we call 'rebel environmental governance' (REG+). This refers to rebel actions aimed at protecting or managing the natural environment to affect civilian welfare amidst increasing pressures of climate change. A framework is advanced for understanding why rebels engage in environmental governance and the implications for security and climate governance. The Element brings rebel organizations into the conversation on climate change, highlighting their role in areas where state power is contested, weak, or absent. This title is also available as Open Access on Cambridge Core.