Unmanned combat air vehicles-i.e. ?drones?-have become a prominent instrument in US efforts to counter objective (and subjective) cross-border terrorist threats with lethal force. As a result, critical questions abound on the legitimacy of their use. In a series of multidisciplinary essays, this book explores the question of legitimacy through the conceptual lenses of legality, morality and efficacy, and then closes with the consideration of a policy proposal aimed at incorporating all three indispensable elements.