The basic control architecture for flexible aircraft is introduced. Both linear and nonlinear optimal control methods are considered in a sequential manner. First, the theory of linear-quadratic regulators is described, and applied to simple aeroelastic problems. A linear estimator is then introduced thus resulting in linear quadratic Gaussian (LQG) control, which is also exemplified. Finally, the approach is expanded to nonlinear problems with a short introduction to model predictive control theory and its application to flexible aircraft. Some recent numerical results are included to illustrate the potential of this technique.