License plate readers (LPRs) have spread rapidly in policing and are now used by an estimated two-thirds of large agencies in the United States (as well as many small agencies) for a range of patrol, investigative, and security operations.¹ Although LPRs have been shown to increase arrests and recoveries of stolen vehicles, their wider impacts on crime prevention and investigations are unclear, as the rigorous evaluation of LPRs has been very limited. Outcomes from LPR use are likely to depend on several factors, including the volume of LPR deployment, the manner in which LPRs are deployed (mobile versus fixed), the types of data accessed by LPR systems, how officers use LPRs in the field, how data are saved and used for investigations, and the public’s reaction to LPR use. Hence, there is a strong need to build an evidence base to guide law enforcement decisions on LPR acquisition and use. With support from the National Institute of Justice, the authors have conducted two new field studies of LPR use in patrol and investigations.²