Rather than using either reported crime or arrests alone to measure changes in crime, the Wilmington Crime Index looks at how both reported crime and arrests change in relation to each other over time. When used with a chronology of the crime-reduction strategies that were implemented for a given year, the maps of the Index show how policing activities impacted crime at the neighborhood level. To date, the Index has been limited to drug crime in Wilmington, but the technique can be adapted for other crimes as well. Drug-related calls for police service were used as a proxy for reported drug crime, because it has been relatively easy to acquire timely data; however, a flaw in using calls-for-service data is that the actual incidence of illicit drug activity in a given area may not necessarily correlate with what residents observe. To reduce this potential for error, the calls-for-service data are cross-checked with corresponding Uniform Crime Reporting drug complaints as they become available. The production of each Index map requires at least 2 years of data for both calls for service and arrests. The difference in the number of calls or arrests from one year to the next is calculated for each reporting area, then the difference in the number of calls for each reporting area is compared with the difference in the number of arrests. The end result is a per geographic unit (reporting are) comparison of the 1-year difference in the number of reported incidents versus the 1-year difference in the number of arrests. Over time, an informative data series is developed. Examples are provided to demonstrate how the Wilmington Crime Index was used to reduce illicit drug activity in the city as part of the evaluation of Wilmington's Weed and Seed initiative. 1 table and 4 figures