Springing from decades of abuse by law enforcement and an excessive criminal justice system, members of over-policed communities lead the current movement for civil rights in the United States. Activated by injustice, individuals protested police brutality in Ferguson, campaigned to end stop-and-frisk in New York City, and advocated for restorative justice in Washington, D.C. Yet, scholars focused on the negative impact of punitive policy on material resources, and trust in government did not predict these pockets of resistance, arguing instead that marginalizing and demeaning policy teaches individuals to acquiesce and withdraw. Mobilized by Injustice excavates conditions under which, despite otherwise negative outcomes, negative criminal justice experiences catalyze political action. This book argues that when understood as resulting from a system that targets people based on race, class, or other group identifiers, contact can politically mobilize. Negative experiences with democratic institutions predicated on equality under the law, when connected to a larger, group-based struggle, can provoke action from anger. Evidence from several surveys and in-depth interviews reveals that mobilization as result of negative criminal justice experiences is broad, crosses racial boundaries, and extends to the loved ones of custodial citizens. When over half of Blacks and Latinos and a plurality of Whites know someone with personal contact, the mobilizing effect of a sense of injustice promises to have important consequences for American politics.