The authors discuss the application of expert systems programming techniques to the design of lead-lag compensators for a linear, single-input/single-output, continuous-time plant. A design method based on first adjusting the high-frequency response with lead and constant-gain compensators followed by adjusting the low-frequency response with lag compensators has been developed. This design heuristic is presented and its ability to achieve specifications for a range of different plants is discussed. The heuristic has been implemented using the production rule knowledge representation; examples of production rules are given and their use is discussed. Inference-engine capabilities and extensions to a conventional analysis and design package, required to implement this automatic control system design method, are also outlined.