Expert systems are computer programs together with databases which attempt to simulate the problem solving and decision making processes of a human expert. This book presents an analysis of the use and development of expert systems for reference and information retrieval. It is directed at librarians and other information professionals and students of reference and information retrieval who already have an understanding of reference service and automated retrieval but have very little knowledge of expert systems. The book provides the necessary background information needed to evaluate the various aspects of expert systems, such as ease of use, source of information, utility within a given environment etc. A brief history and basic overview of artifical intelligence is followed by a description of the basic components of an expert system showing the ways in which they interact. Some of the more interesting attempts to develop systems which emulate some or all of the functions performed by online searchers and reference librarians are discussed. The processes involved in human cognition, expert behaviour, knowledge representation using computer systems, user interfaces, design of both large and small scale systems are all covered. Finally a scenario of future systems for reference and information retrieval is presented.