This is the expanded version of the earlier highly successful book, "Fuzzy Sets, Uncertainty and Information", reflecting the tremendous advances that have taken place subsequently. The primary purpose of this book is to provide the student with a comprehensive coverage of theoretical foundations of fuzzy set theory and fuzzy logic as well as a broad overview of the increasingly important applications of these novel areas of mathematics. No previous knowledge of fuzzy sets or fuzzy logic is required. Basic ideas such as neural networks, general algorithms and rough sets are also explained.Throughout the book, examples are used to illustrate concepts, methods and generic applications as they are introduced. Extensive and carefully selected bibliography, together with bibliographical notes at the end of each chapter and a bibliographical index, is an invaluable resource for further study of fuzzy theory and applications. Each chapter is followed by a set of exercises, which are intended to enhance an understanding of material presented in the chapter."It should be on the desk of everyone who is intended in acquiring a solid understanding of the foundations of fuzzy sets and fuzzy logic and the competence that is needed to apply them to the solution of real-world problem."Lotfi A. Zadeh in his Foreword to the book.