Most legal expert systems attempt to implement complex models of legal reasoning. This book argues that a complex model is unnecessary. It advocates a simpler, pragmatic approach in which the utility of a legal expert system is evaluated by reference, not to the extent to which it simulates a lawyer's approach to a legal problem, but to the quality of its predictions and of its arguments. The author describes the development of a legal expert system, called SHYSTER, which takes a pragmatic approach to case law. He discusses the testing of SHYSTER in four different and disparate areas of case law, and draws conclusions about the advantages and limitations of this approach to legal expert system development. Chapter 1 presents a critical analysis of previous work of relevance to the development of legal expert systems. Chapter 2 explains the pragmatic approach that was adopted in the development of SHYSTER. The implementation of SHYSTER is detailed using examples in chapter 3. Chapter 4 describes the testing of SHYSTER, and conclusions are drawn from those tests in chapter 5. Examples of SHYSTER's output are provided in appendices.