Political movements are an increasingly common form of mass political mobilization, and the legitimacy and authority of democratic states depends to a growing extent on the relationship between movements and states. Existing case studies of political movements neglect that relationship in favor of issues of mobilization, organization, and societal impact. These studies can nonetheless be used to show that political movements employ a mixture of confrontation and collaboration in their relationship to the state. More centralized states, which offer fewer institutional channels for movement influence, face more confrontational movements. However, political movements in all democratic settings use confrontation primarily as a strategic device to enhance their leverage in negotiations with state authorities. Movements are not a challenge to state authority so much as they are a force for change within democratic society.