This article depicts the transition, in Quebec, between 1763 and 1968, from a communitarian model of police, where this public function is performed from within by the members of the community, to a liberal model of police, where the responsibility to preserve public order is assumed by government controlled exogenous structures. This transition occurs in two successive movements, each of them following the same goal, namely, to persuade that the public force of coercion is used exclusively in the pursuit of the common good. During the first movement, in the first half of the 19th century, the police function is dissociated from the economic power. During the second movement, in the course of the 20th century, the police function is formerly separated from the political power, owing to the emergence of the concept of expertise in maintaining public order.