This is release 1.0 of the National Water-Quality Assessment (NAWQA) Area-Characterization Toolbox. These tools are designed to be accessed using ArcGIS Desktop software (versions 9.3 and 9.3.1). The toolbox is composed of a collection of custom tools that implement geographic information system (GIS) techniques used by the NAWQA Program to characterize aquifer areas, drainage basins, and sampled wells.