This chapter proposes a high-order FAS approach for a generalized form of nonaffine strict feedback systems (SFSs). Firstly, a generalized form of first-order nonaffine SFS is introduced, and a recursive solution is proposed to transform equivalently it into a high-order FAS model under certain common assumptions. Particularly, two special cases for first-order nonaffine SFSs are studied, and their recursive results are directly obtained based on the generalized results. Secondly, the FAS approaches for second- and mixed-order nonaffine SFSs are also presented. It is shown that, using the feature of FAS models, the control design for the class of generalized nonaffine SFSs can be easily realized and better solved in the sense of providing an LTI closed-loop system with a desired eigenstructure. Lastly, illustrative examples are worked out to demonstrate the design procedure and show the efficacy of the proposed approach.