This paper extends Tyler's procedural justice model of public compliance with the law. Analysing data from a national probability sample of adults in England and Wales, we present a new conceptualization of legitimacy based on not just the recognition of power, but also the justification of power. We find that people accept the police's right to dictate appropriate behaviour not only when they feel a duty to obey officers, but also when they believe that the institution acts according to a shared moral purpose with citizens. Highlighting a number of different routes by which institutions can influence citizen behaviour, our broader normative model provides a better framework for explaining why people are willing to comply with the law.