Although hot spots policing has become one of the most promising policing strategies, the empirical evidence on the effectiveness of hot spots policing does not suggest what police should be doing in crime hot spots. To date, police enforcement actions – pedestrian investigations, traffic enforcement, and arrests – still dominate American policing. Yet empirical studies of these actions have not: focused on micro-geographic areas, employed multiple measures of police enforcement actions, or empirically compared the effectiveness of different enforcement actions. Given these gaps in the literature, a mixed-methods study sought to answer four research questions. (1) Do four police enforcement actions focused on offenders or potential offenders reduce violent crime in hot spots? The four police enforcement actions examined were pedestrian investigations, traffic enforcement events, quality of life arrests, and violent crime arrests. (2) Are any one of these four police enforcement actions more effective than the others? (3) When police commanders allocate resources to crime hot spots, what do police commanders think they are doing? (4) What are police commanders’ rationales for what they do in crime hot spots? The first two questions were answered using official data from the Philadelphia Police Department. A purposive sample of 169 high crime street blocks and intersections was drawn and longitudinal data analyses examined the effects of police enforcement actions on monthly violent crime counts from 2009 to 2013 (n = 10,140). Wald Tests were used to test for the differential effectiveness of the four enforcement actions. Qualitative methods answered the remaining two research questions. Field observations of crime strategy meetings (May, 2014 to August, 2014) and interviews with police commanders (November, 2014 to February, 2015) were conducted. The quantitative results found total enforcement and pedestrian stop levels in the previous or same month linked to higher expected monthly violent crime counts. The positive effect of pedestrian stops was significantly larger than the effects of traffic enforcement or quality of life arrests. Despite the positive relationship between police enforcement and violent crime, the qualitative results provided insight into what police commanders thought they were doing in crime hot spots. Three themes emerged from the qualitative data: (1) “locking down” crime hot spots, (2) disrupting high risk offenders, and (3) educating potential victims. Police commanders rationalized these beliefs with four explanations of their effectiveness: (1) making offenders “think twice”, (2) denying potential offenders and victims certain places in order to reduce crime opportunities, (3) getting high risk offenders “off the street”, and (4) target hardening. Drawing on theorizing for how police enforcement actions might actually link to higher levels of crime (Grabosky, 1996) and methodological concerns raised by Taylor (2015), five possible explanations for the observed positive relationships among police enforcement actions and violent crime are provided: (1) an anticipatory effect, (2) over-deterrence, (3) escalation, (4) unintended enticement and self-fulfilling prophecies, and (5) temporal scaling. The anticipatory effect explanation centers on the police correctly anticipating outbreaks of violent crime but violent crime still not being reduced due to (1) dosage, (2) the overuse of enforcement, (3) police legitimacy, (4) temporal displacement or two components the study’s design (5) imprecise measurement and (6) lack of a proper counterfactual. Additionally, police enforcement actions may inadvertently reduce guardianship though over-deterrence, escalate competition among rival offenders, or inform potential offenders of crimes they could or “should” be committing. Finally, the study’s temporal scale (i.e., months) may not be fine enough to capture the actual cycling of how increased enforcement actions produce lower violent crime levels. The qualitative data are drawn upon to possibly support these explanations. Additionally, the pros and cons of police commanders’ perspectives on the use and effectiveness of enforcement actions are discussed in context of the criminological theory and crime control literatures. Finally, the results are discussed in terms of their implications for crime control theory and policy. / Criminal Justice