The issues that must be evaluated by persons both in the U.S. Environmental Protection Agency (U.S. EPA) and in firms contracted for environmental remediation work present many complex and difficult problems. The amount of specialized information that must be evaluated as part of higher-level decision processes is expanding. At the same time, there is a scarcity of persons with adequate training and experience to evaluate all of the data required to make appropriate decisions. The situation has created a need for increasing application of automated decision support software. The EPA Risk Reduction Engineering Laboratory (RREL), formerly the Hazardous Waste Engineering Research Laboratory, was one of the early participants in knowledge system development and evaluation within the U.S. EPA. Some of the history of this group's work, the nature of the decision processes conducted within Agency, and the relationship between these processes and the knowledge-based system work at RREL are discussed in the paper. In broader scope, the paper discusses the current status of expert systems in the Agency and the projected future of knowledge-based applications within the community of environmental engineers, scientists, and regulators.