Since the T-S fuzzy model is proposed by Takagi and Sugeno, research on the one has achieved fruitful results, which have been successfully applied in practical engineering fields. In addition, uncertainties are widely present in dynamic system models, and external unknown factors inevitably act on actual engineering systems, as well as actuators, sensors, and system components suffering from failures without warning, the above mentioned events will lead to the deterioration of system performance, and even cause instability of the system, resulting in unexpected economic losses and casualties. Robust filtering and fault diagnosis provide an effective way to improve the reliability and security of control systems, and related research has attracted much attention. However, it should be pointed out that although many achievements have been made in research on the above-mentioned issues, there are still many problems that need to be further addressed. On the basis of the existing research on T-S fuzzy theory, robust filtering theory, and fault diagnosis theory, the robust filtering and fault diagnosis problems of a class of T-S fuzzy systems are studied in this book.