In this thesis, model reference output tracking control of unmanned aircraft vehicles are aimed. The control problem is complicated due to the lack of accurate knowledge of nonlinear system dynamics and additive state-dependent nonlinear disturbancelike terms. Only the output of the vehicle is considered to be available for control design purposes. A novel robust controller is designed that ensured a global asymptotic stability result. In the design of the controller, proportional integral controller is fused with the integral of the signum of the tracking error to compensate uncertainties. Lyapunov type stability analysis are utilized to prove asymptotic convergence of the output tracking error. Extensions to optimal, adaptive and neural network controllers are also designed. Simulation and experiment results are presented to illustrate the performance of the robust controllers.