The book includes a solid and comprehensible introduction to the fundamental concepts of fuzzy set theory, a detailed discussion of rule-based, relation-based, and logic-based calculi for approximate reasoning, as well as an overview of common fuzzy programming languages. The author describes architectural principles that allow for the efficient utilization of the degrees of freedom in fuzzy set theory. Furthermore, a new fuzzy programming system based on the explained concepts is presented, which enables the development of complex applications due to its rich repertoire of fuzzy operators and inference mechanisms, as well as its object-oriented architecture.