In this chapter, two types of high-order strict feedback system (SFS) models with parametric uncertainties are introduced, namely, the second- and high-order SFS models, which possess a common full-actuation structure. Using the direct design approaches for adaptive stabilizing controllers and adaptive tracking controllers of FAS models proposed in Chapter 5, direct second- and high-order backstepping methods for the designs of adaptive stabilizing controllers of the second- and high-order SFSs with parametric uncertainties are also proposed. These approaches do not need to convert the high-order systems into first-order ones, and are thus more direct and effective. Furthermore, for a specific second- or higher-order SFS, application of the proposed high-order backstepping methods needs fewer steps than the usual first-order backstepping method, thereby saving much design and computation complexity.