Most of the important elements of police work cannot be measured and compared. Furthermore, the theme of efficacy in police work is often neglected because of the emphasis on efficiency. Following the theories of Robert Peel, the author defines the fundamental role of the police as prevention of crime and disorder without use of repressive measures and military force. The police must also seek to gain the voluntary cooperation of the public. This cooperation is inversely proportional to the strength of the police force. Finally, the police must be considered the public and the public the police. The ultimate proof of police effectiveness is the absence of crime and disorder in the community. Sociologists have noted the difficulty of finding criteria which measure effectiveness and efficiency. Police chiefs are aware of this problem because they must hire and train the officers who are to perform the work of the police force. Educational norms for officers are deemed important since the quality of the force depends on the efficacy of the police sergeant or officer. The author raises the possibility of a modular teaching program that could be applied in any region of the country. In conclusion, the need for studying the views of earlier members of the police profession rather than only analyzing data is emphasized. No references are cited. -- in French.