In recent years “leaderless” social movements have proliferated around the globe, from North Africa and the Middle East to Europe, the Americas, and East Asia. Some of these movements have led to impressive gains: the toppling of authoritarian leaders, the furthering of progressive policy, and checks on repressive state forces. They have also been, at times, derided by journalists and political analysts as disorganized and ineffectual, or suppressed by disoriented and perplexed police forces and governments who fail to effectively engage them. Activists, too, struggle to harness the potential of these horizontal movements. Why have the movements, which address the needs and desires of so many, not been able to achieve lasting change and create a new, more democratic and just society?