The typology of regressive outcomes flows from crime prevention policies and includes such phenomena as escalation, overdeterrence, and the generation of perverse incentives. In the area of escalation, some strategies designed to combat crime actually produce crime. Further, some countermeasures may directly or indirectly lead to collateral damage of greater magnitude than that resulting from the target behavior. Escalation may also involve unintentional enticement, reversal of effects, labeling, and under-enforcement. Crime displacement is perhaps the most familiar unintended consequence of crime prevention. The risk that undesirable activity will be shifted into other areas has become part of conventional criminological wisdom. In some cases, crime prevention measures or threatened sanctions may have a detrimental effect on legitimate activity, thus resulting in over-deterrence. Finally, crime prevention policies may be structured in such a way as to cause perverse incentives. Moral hazard, the propensity of persons insured against risk to engage in risk-taking behavior, and vulnerability to victimization are discussed. The etiology of negative externalities is explained in terms of such parameters as planning and implementation failures. Principles and safeguards are suggested to reduce the risk of unintended consequences of crime prevention. 90 references, 21 notes, and 1 table