In free and democratic societies, police are a contradiction. Their authority and capacity to coerce and overpower resistance is at odds with the ideal of liberty, and their broad discretion to use this authority selectively is at odds with the ideal of equality. Nevertheless, as the primary coercive agents of the state, they are expected to protect those ideals in order to maintain the state’s monopoly on legitimate violence. In the United States, this contradiction has placed police at the center of controversy of all types, torn between an array of the conflicting interests of a diverse and multicultural society. To regulate the opposing pressures and demands placed upon them, police have increasingly through history embraced a law enfor...