To analyze these reports, a theoretical framework was developed: the prevention model. This framework is based on a probabilistic choice model and defines three aspects of a crime prevention measure. These are orientation (situation, person or offense oriented); range (the spectrum of possible crime situations of potential offenders and of offenses); and strategy (influencing the potential offender with respect to his perception of the profits resulting from crime, the required effort, the possible sanction, the chance of receiving a sanction, and his moral standards). Data were obtained on 280 prevention measures and 106 measurements of the effects on criminality. The total group of prevention measures is systematically described using the prevention model. Most (73 percent) of the measures are situation-oriented, but a significant minority (36 percent) are person-oriented. Findings provide an overall impression of the quality of the measurements on the effects of prevention measures on crime. In 37 percent of the projects, no effort was made to measure such effects. Data indicate that the effect of prevention measures on crime depends on three factors: intensity, seriousness of the crime problem, and strategy. 10 tables and 28 references