Chapter 9 considers the spacecraft attitude control system design problem, in particular, the author focuses on Linear Quadratic Regulator (LQR) method. Two desired frames that are likely the desired spacecraft attitude are considered. Section 9.1 discusses LQR design for nadir pointing spacecraft. This is a standard method which is addressed in Appendix A. Section 9.2 presents an LQR design for inertial pointing spacecraft which has an extremely simple linearized model. Therefore, this design problem can be solved analytically rather than numerically. The relation between the LQR design and the closed-loop pole positions is establish. It is indicated that the analytical solution provides insight for engineers to trade off many conflict requirements. It is shown that the design globally stabilizes the nonlinear spacecraft system even the design is based on the linearized system. In section 9.3, it is proved that the LQR design discussed in section 9.2 is actually a robust pole assignment design. Therefore, the design is insensitive to the modeling error and is good for disturbance rejection.