One of the central pillars of US counterterrorism policy is that capturing or killing a terrorist group's leader is effective. Yet this pillar rests more on a foundation of faith than facts. In Leadership Decapitation, Jenna Jordan examines over a thousand instances of leadership targeting—involving groups such as Hamas, al Qaeda, Shining Path, and ISIS—to identify the successes, failures, and unintended consequences of this strategy. As Jordan demonstrates, group infrastructure, ideology, and popular support all play a role in determining how and why leadership decapitation succeeds or fails. Taking heed of these conditions is essential to an effective counterterrorism policy going forward.