Growing concerns about the vulnerability of the electric grid, uncertainty about the cost of oil, and an increase in the deployment of renewable generation on domestic military installations have all led the Department of Defense (DoD) to reconsider its strategy for providing energy security for critical domestic operations. Existing solutions typically use dedicated backup generators to service each critical load. For large installations, this can result in over 50 small generators, each servicing a low voltage feeder to an individual building. The system as a whole is typically not well integrated either internally, with nearby renewable assets, or to the larger external grid. As a result, system performance is not optimized for efficient, reactive, and sustainable operations across the installation in the event of a power outage or in response to periods of high stress on the grid. Recent advances in energy management systems and power electronics provide an opportunity to interconnect multiple sources and loads into an integrated system that can then be optimized for reliability, efficiency, and/or cost. These integrated energy systems, or microgrids, are the focus of this study. The study was performed with the goals of (1) achieving a better understanding of the current microgrid efforts across DoD installations, specifically those that were in place or underway by the end of FY11, (2) categorizing the efforts with a consistent typology based on common, measurable parameters, and (3) performing cost-benefit trades for different microgrid architectures. This report summarizes the results of several months of analysis and provides insight into opportunities for increased energy security, efficiency, and the incorporation of renewable and distributed energy resources into microgrids, as well as the factors that might facilitate or impede implementation.