Is killing or capturing insurgent leaders an effective tactic? Previous research on interstate war and counterterrorism has suggested that targeting enemy leaders does not work. Most studies of the efficacy of leadership decapitation, however, have relied on unsystematic evidence and poor research design. An analysis based on fresh evidence and a new research design indicates the opposite relationship and yields four key findings. First, campaigns are more likely to end quickly when counterinsurgents successfully target enemy leaders. Second, counterinsurgents who capture or kill insurgent leaders are significantly more likely to defeat insurgencies than those who fail to capture or kill such leaders. Third, the intensity of a conflict is likelier to decrease following the successful removal of an enemy leader than it is after a failed attempt. Fourth, insurgent attacks are more likely to decrease after successful leadership decapitations than after failed attempts. Additional analysis suggests that these findings are attributable to successful leadership decapitation, and that the relationship between decapitation and campaign success holds across different types of insurgencies.