These chapters are relatively extensive. At their beginning is mentioned AND, OR and NOT generalization. Then is established fuzzy diagnostic system from the fuzzification over establishing inference up to defuzzification. There are demonstrated individual defuzzification methods and enumerated their advantages and disadvantages. Defuzzification methods are also demonstrated on concrete examples in MATLAB. In other parts is shortly describe MATLAB´s fuzzy toolbox. And there is also describe Mamdani fuzzy system and Sugeno-Takagi system. Very important is part about fuzzy system tuning, because it is one of the most demanding operations in practice. At the close are defined inputs and outputs terms in all forms. Chapters are close by enumeration of usability fuzzy algorithms in practice.