The United States increasingly relies on unmanned aerial vehicles to target insurgent and terrorist groups around the world. This monograph analyzes the available research and evidence that assesses the political and military consequences of drone strikes. It is not clear if drone strikes have degraded their targets, or that they kill enough civilians to create sizable public backlashes against the United States. Drones are a politically and militarily attractive way to counter insurgents and terrorists, but, paradoxically, this may lead to their use in situations where they are less likely to be effective and where they are difficult to predict consequences.