This chapter describes the emergence of policing as an institutional mechanism for maintaining order in increasingly urban social contexts. Through a review of prior literature, we identify three impediments to police effectiveness – autonomy, capacity, and principal–agent problems – and explain the ways in which poor performance undermines citizens’ trust in police and willingness to cooperate. Then, using data from citizen and officer surveys, we illustrate the ways in which a lack of trust between citizens and the police undermines effective policing across the six countries that are the focus of this study.