Criteria for productivity are difficult to establish the number of arrests is not significant without considering the types of crimes involved, and public satisfaction is not always a measure of effective services. For each productivity indicator there are one or several factors which affect its validity. The form of productivity must also be considered, as the goals of specialty units are frequently given priority over general police goals. Frequently, performance measures such as response time have little to do with actual results even though there appears to be a logical association between the indicator and the results. As a consequence, researchers tend to perpetuate myths of the police profession in their choice of indicators. At the same time, however, researchers may also establish the ineffectiveness of a particular strategy (e.g., preventive patrols). Thus, the essential question for empirical research involves what the police must do to satisfy the multiple and variable public needs of the moment. Research can aid the police in deciding which technology to apply, in determining what legal restrictions apply to the police, in comparing different police functions to assess cost effectiveness, and in making varied decisions. However, police functions range from crime prevention to protection of constitutional rights, and research has tended to focus only on one aspect of police responsibilities (i.e., crime control). Little importance has been attached to measuring productivity in non-crime-related activities; as a result, police tend to neglect other activities that will go unrecognized. Thus, a good deal of the research on police productivity has been unproductive or counterproductive, and researchers should devote a large portion of their efforts to assessing actual and possible police activities not related to crime. Extreme caution must be exercised in applying research results because blind acceptance of myths perpetuated by research can place police chiefs in an awkward position. Four notes are supplied. --in French.