In recent years, driven by the demands of combat in Iraq and Afghanistan, as well as looming budgetary the United States Department of Defense has increasingly focused on the ways in which energy affects its operations ortunities to improve its performance through the development and adoption of innovative energy technologies and practices. Many observers see in this new focus exciting opportunities in the intersection of two powerful forces within one institution: the most potent engine of technological innovation in human history, and the unparalleled energy demands of national defense. DoD's historical record on energy innovation is extraordinary, and there is reason to hope that important advances might come froma renewed effort in this area. But there also appear at present to be significant limitations upon the scope and scale of DoD's likely influence on technological advance that can contribute to the nation's energy infrastructure as a whole, and particularly to the development and deployment of low-carbon energy systems that might affect the rate of climate change.