GIS supports four groups of spatial functions: general operations such as the retrieval, classification, and measurement of spatial data; overlay operations that involve adding, removing, or reordering map layers; neighborhood operations that count points or lines contained within polygons; and connectivity functions that generate buffers around points, lines, and areas. Examples of spatial data relevant to law enforcement include point (crime locations); line (streets); and area (precinct boundaries) features. These geographic features are often separated into overlapping thematic layers (schools, parks, political boundaries, criminal offenses, traffic, and 911 calls). GIS provides users the flexibility to combine or separate data into as many or as few layers as needed. The most common approach in law enforcement agencies is to have a crime analyst use GIS to analyze the spatial and temporal factors associated with a series of crimes or to detect patterns, trends, and exceptions. Command-level executive are now using GIS to help decide how to deploy resources and where to locate facilities. This article describes the use of GIS in Waco, Tex., a moderate-sized city far removed from other major metropolitan areas. The Waco Police Department has been using GIS for about 10 years and is currently generating crime analysis bulletins for its patrol officers. This article also provides a short list of crime mapping resources and a glossary of terms.