Ann Macintosh Napier University, UK The papers in this volume are the refereed application papers presented at ES2001, the Twenty-fIrst SGES International Conference on Knowledge Based Systems and Applied ArtifIcial Intelligence, held in Cambridge in December 200 I. The scope of the application papers has expanded over recent years to cover not just innovative applications using traditional knowledge based systems, but also to include applications demonstrating the whole range of AI technologies. These papers continue to illustrate the maturity of AI as a commercially viable technology to solve real world problems. The papers were subject to refereeing by at least two expert referees. All papers that were in any way controversial were discussed in depth by the Application Programme Committee. For the ES2001 Application Stream, a paper is acceptable even if it describes a system that has not yet been installed, provided the application is original and the paper discusses the kind of things that would help others needing to solve a similar problem. Papers have been selected to highlight critical areas of success - and failure - and to present the benefIts and lessons learnt to other developers. This volume contains sixteen papers describing deployed or emerging applications in a range of diverse areas: business and commerce, engineering, manufacturing, knowledge and information management, and music.