The paper identifies what features a good classification system needs, including clear and simple definitions, formal properties, comprehensiveness, nonrestrictiveness, and theoretical basis. Starting from basics, a definition of crime prevention is presented from which paradigmatic models of the criminal event and crime prevention itself are developed. The definition centers around causal mechanisms operating in the proximal circumstances of criminal events, that is, the situation plus the offender's disposition. Only at this point can the classification system be introduced, on the platform of a minimal theory of criminal events that encompasses a range of relevant disciplines (law, psychology, sociology, and ecology). The classification system is not a single rigid taxonomy but rather a tool that can generate alternative classifications and descriptions of crime prevention actions. The classification system and paradigms are presented in part to stimulate discussion and further system refinement. 35 references, 4 notes, and 3 figures