This chapter focuses on the mechanisms of policing and punishment that developed in mid-nineteenth-century slave cities, which seeks to develop two lines of enquiry. It outlines key features of slave law enforcement in cities and situates the policing of urban nonsla-veholders, particularly poor whites, as a central part of the story of slave control. The chapter adds a transnational perspective through a comparative analysis of urban slavery, policing and punishment in the United States and Brazil. It proposes that while the policing of slaves shared notable commonalities throughout the urban Americas, the policing of white nonslaveholders in cities proceeded along very different lines and in ways that generated particular ideological and political challenges for the pro-slavery arguments that developed in the pre-Civil War southern United States. In the slave cities of the United States, formalised law enforcement enhanced and often entirely replaced the surveillance and disciplinary power of individual slaveholders.