Pathways for exposure of birds to pesticides include soil, water, air, soil-dwelling organisms, and insects. A process approach to avian exposure calculates transport and transformation of agricultural chemicals through each of the exposure media. Differential equations calculating the time rate of change of chemical in each exposure medium are solved in this approach. Development of terrestrial exposure algorithms at the United States Environmental Protection Agency (U.S. EPA), Environmental Research Laboratory, Athens, GA, draws on validated technology where well-established methodologies do not exist. Supporting data for soils, meteorology, crops and cropping scenarios, and species distribution data are being developed on a regional scale based on the 186 major land resource areas (MLRA) defined by the United States Department of Agriculture (USDA). This chapter further describes the process-oriented, mechanistically based approach to avian exposure calculations, the supporting databases required for doing regional analyses, and the interactive system design for accessing this information.