Expert systems are a promising computer-based approach to helping environmental engineers solve difficult problems. A number of such systems have been developed to date in the areas of hazard assessment, modeling support, process failure diagnosis, and regulatory support. The US Environmental Protection Agency has several programs underway to introduce the technology into its operations. Five systems are being developed that support the review of applications for operating permits for RCRA hazardous waste facilities and selection of remedial action alternatives at Superfund cleanup sites. The most highly developed of these is FLEX, a program that evaluates the chemical resistance of synthetic liners exposed to wastes contained in landfills and impoundments. Work on FLEX and other systems has identified a number of issues important to successful implementation of expert systems within an organization such as EPA.