Since its inception, the theory of fuzzy sets has advanced in a variety of ways and in many disciplines. Applications of fuzzy technology can be found in artificial intelligence, computer science, control engineering, decision theory, expert systems, logic, management science, operations research, robotics, and others. Theoretical advances have been made in many directions. The primary goal of this book is to provide an introduction to fuzzy set theory and to also act as a textbook. To balance the character of a textbook with the dynamic nature of this research, references have been added to develop a deeper understanding for the interested reader. The text updates the research agenda with chapters on possibility theory, fuzzy logic and approximate reasoning, expert systems, fuzzy control, fuzzy data analysis, decision making and fuzzy set models in operations research. Chapters have been updated and extended, exercises are included, and a teacher's manual is available upon request.