It makes sense to design police policies and practices on a foundation of research that shows some policing practices to be more effective than others in achieving specific goals of public safety; however, research and science have limits; some are technical and other are more philosophical. A police policy and practice scientifically proven effective in one jurisdiction, for example, may not be as effective or practical in another jurisdiction due to various factors. Also, based on its own precepts, scientific knowledge is always tentative and subject to change based on additional research. Some examples of such evolution in policing research are provided in this paper. Given the reality of both the benefits and tentativeness of police research, this paper offers six principles for police leaders to follow. First, keep up- to-date on the latest police research and evidence-based practices. Second, assess relevant studies to determine their applicability to your own jurisdiction. Third, guard against valuing only those studies that confirm what one currently believes. Fourth, conduct scientific studies in one‘s own jurisdiction to determine what works best there. Fifth, ongoing measurement of the effects of policy and practice is needed for continuous improvement, Sixth, remember that a practice that achieves one benefit while also producing an adverse effect must be improved.