This volume is the ideal introduction to environmental expert systems. Its opening chapter gives a broad overview of the area of environmental expert systems, including the legal issues associated with these systems. An appendix to this chapter surveys the available systems, providing the function, status, and developer for each, as well as the software and hardware necessary to run them. Over 65 of the 80 available systems are covered, including GEOTEX, CORA, CADRA, Risk*Assistant*, and Fish Toxicity Prediction. Broader issues, such as success factors for expert systems, verification and validation of environmental expert systems, and the future of environmental expert systems at EPA, are also covered.