The ultimate goal of the Control engineer is to design feedback systems (also called controllers) that force the plant to conform to a desired behavior. Moreover, feedback can achieve the specification even with disturbances and imprecise knowledge of the plant. One class of models for which both analysis and design are well understood by Control and Stability Engineers is the class of linear time-invariant plants. A central goal of this book is the successful application of the Linear Quadratic Gaussian (LQG) control approach to a highly aerodynamically unstable Expendable Launch Vehicle (ELV) and also the demonstration of an alternative design using Fuzzy Logic Control, with the classical Proportional Integral and Derivative (PID) controller as a benchmark. Up to the time of writing this book, Controllers designed from any established means come with no guarantee on nominal stability, stability robustness or command-following. Rather any such properties are inferred from extensive computer simulations. In order words, a complete and systematic design methodology is yet to emerge.