Second Generation Expert Systems have been a very active field of research during the last years. Much work has been carried out to overcome drawbacks of first generation expert systems. This book presents an overview and new contributions from people who have played a major role in this evolution. It is divided in several sections that cover the main topics of the subject: - Combining Multiple Reasoning Paradigms - Knowledge Level Modelling - Knowledge Acquisition in Second Generation Expert Systems - Explanation of Reasoning - Architectures for Second Generation Expert Systems. This book can serve as a reference book for researchers and students and will also be an invaluable help for practitioners involved in KBS developments.