This article explore the relationships between trust, knowledge and expertise in matters of policing. Firstly, the author analyses different models of police action, in light of the results of empirical studies on policing published since 1960, and that he groups in three main tendencies according to their way of seeing the relationship between citizens and the police. Secondly, he examines how the police can enhance the public’s trust towards itself and improve mutual relationships of trust between citizens. The author concludes by proposing criteria aimed at recognising the democratic character of a police force.