This handbook explains the importance and practice of using a geographic information system (GIS) in designing and implementing an effective response to large-scale disasters, including wildfires, hurricanes, earthquakes, and terrorist attacks. The handbook is organized according to the accepted methodology of disaster management, which involves planning and identification, mitigation, preparedness, response, and recovery. The first three stages involve tasks that an organization or community can perform before a disaster occurs. The latter two tasks focus on postdisaster efforts. The spatial display and analysis tools of GIS are ideal for assessing disaster risks, consequences, and responses. GIS can display the location, size, value, and significance of assets that may be impacted by disasters. It can show the kinds of environmental, atmospheric, and other conditions that contribute to particular kinds of natural disasters. GIS can also juxtapose a particular kind of asset with specific hazardous conditions over a wide geographic area, thus allowing a precise calculation of potential loss in the immediate area. With this kind of graphic depiction, the choices about what to do and where to do it are clarified for those charged with making fast, cost-effective decisions. This handbook details how GIS software features can be used at each stage of planning and response. The use of GIS in a disaster is illustrated by its application in New York City in the days after September 11, where it was used to provide assistance to rescue and recovery teams. The manual also profiles GIS-based disaster modeling software packages now available at no cost to local communities.