Citing evidence on intercity differences in crime rates, as well as differences in rates of increase for several kinds of crime, this paper argues that police departments differ in their effectiveness. The key to an understanding of effectiveness lies in the way police departments themselves are organized. How individual police men perform their occupational duties depends in part on how these duties are defined. In order to understand these definitions and the pressures which affect the way police perform their work, it is necessary to adopt a "systemic" view of legal and illegal forces in society. Determinants of police effectiveness are ex plored, through examples from the control of organized crimes, by relating the way departments interact with other legal and illegal organizations.