The four police actions at issue in this study were pedestrian investigations, traffic enforcement, quality-of-life arrests, and violent-crime arrests. The study found that a standard deviation increase in total enforcement in the focal month was linked to significantly higher levels of violence (16-40 percent) across all of the models. Pedestrian stops were consistently linked to higher levels of violent crime across all models. Explanations for this finding focus on the anticipatory effect, over-deterrence, escalation, unintended enticement and self-fulfilling prophecies, and temporal scaling. The pros and cons of police commanders' perspectives on the use and effectiveness of enforcement actions are discussed in the context of the criminological theory and crime-control literatures. Police commanders viewed the four tactics as achieving the following objectives: "locking down" crime hot spots; disrupting the criminal behaviors of high-risk offenders; and educating potential victims. The study results are discussed in terms of their implications for crime-control theory and policy. The findings suggest that efforts to reduce crime in hot spots cannot be narrowly focused on law enforcement actions. Comprehensive efforts must include situational crime prevention and attention to the multifaceted causes and remedies for criminal behavior concentrated in ;particular geographic areas. Extensive tables and figures and approximately 300 references