This volume contains the most significant papers written by L. A. Zadeh, who in 1965 introduced the concept of a fuzzy set. Fuzzy set theory has become the foundation for the development of the fields of artificial intelligence and expert systems, especially in the applications of knowledge-based systems. As such, Zadeh's work has influenced researchers around the world. Zadeh has cooperated with editors in choosing the papers presented here, and the editors have provided an introduction for each paper. Topics covered include probability measures of fuzzy events, similarity relations and fuzzy orderings, a fuzzy-algorithmic approach to the definition of complex or imprecise concepts, and much more.