This chapter introduces an active fault-tolerant control (AFTC) framework tailored for high-order fully actuated systems (FASs) with parameter uncertainties. Beginning with the formulation of nonlinear measurement-based uncertain faulty FAS models, the benefits of this representation are systematically demonstrated through Lie derivative analysis. An integrated FAS adaptive observer-controller mechanism is constructed, from which a closed-loop dynamic data modeling framework is subsequently developed. This structure uncovers the dynamic characteristics including fault features, and naturally yields a fault detectability condition. Leveraging the fault diagnosis model, an AFTC methodology is formulated, thereby extending the theoretical foundation of FASs. The uniform bounded stability is rigorously validated through mathematical proof and experimentally confirmed via case studies.