Linlin Li addresses the analysis and design issues ofobserver-based FD and FTC for nonlinear systems. The author analyses theexistence conditions for the nonlinear observer-based FD systems to gain adeeper insight into the construction of FD systems. Aided by the T-S fuzzytechnique, she recommends different design schemes, among them the L_inf/L_2type of FD systems. The derived FD and FTC approaches are verified by twobenchmark processes.