Nuclear deterrence is sometimes treated as a known quantity—a definite thing that keeps us safe and ensures our security. It has also often been used as a justification for possessing nuclear weapons. Nuclear deterrence, however, is based on an unexamined notion: the belief that the threat to destroy cities provides decisive leverage. An examination of history (including recent reinterpretations of the bombing of Hiroshima) shows that destroying cities rarely affects the outcome of wars. How is it possible that an action that is unlikely to be decisive can make an effective threat? Recent work on terrorism suggests that attacks against civilians are often not only ineffective but also counterproductive. And a review of the practical record of nuclear deterrence shows more obvious failures than obvious successes. Given this, the record of nuclear deterrence is far more problematic than most people assume. If no stronger rationale for keeping these dangerous weapons can be contrived, perhaps they should be ...