Fuzzy system theory has been successfully applied in many fields. Fuzzy systems can be established according to a given approximation accuracy. They can approximate a predetermined model or control process. Therefore, it is important to analyze the approximation mechanism of fuzzy systems.

The general approximation of a fuzzy system refers to whether the fuzzy system can approximate any continuous function defined on a compact set with arbitrary precision. Currently, the research on fuzzy systems as universal approximators is mainly divided into two aspects. One is qualitative research, that is, the study of the internal mechanism of analyzing the approximation performance of various fuzzy systems; the second is quantitative research, which aims to determine the approximation error of fuzzy systems. Meanwhile, adaptive control is a discipline that studies uncertain system control problems. Adaptive control can be regarded as a feedback control system that can intelligently adjust its own characteristics according to environmental changes so that the system can work in an optimal state according to some set standards. Adaptive control is very successful in the control of aviation, missiles, and space vehicles. Adaptive control, like conventional feedback control and optimal control, is also a control method based on a mathematical model. The only difference is that the adaptive control is based on less prior knowledge about models and disturbances, which requires operation in the system. In the process, the information about the model is continuously extracted to gradually improve the model. It is well known that system uncertainties exist in most actual systems, which are produced by external disturbances, modelling errors, etc. An effective method to handle these uncertainties is using fuzzy logic systems.

The aim of this Special Issue is to collate original research and review articles related to the qualitative and quantitative analysis of fuzzy logic systems, adaptive fuzzy control, and stability analysis of dynamic systems.

Potential topics include but are not limited to the following:

• Application of fuzzy logic systems
• Qualitative and quantitative analysis of fuzzy logic systems
• Fuzzy universal approximator and its applications
• Adaptive fuzzy control
• Stability of nonlinear systems under fuzzy approximation
• Adaptive fuzzy synchronization of chaotic systems
• Fractional-order fuzzy adaptive control