The ship roll stabilization by active anti-heeling tanks operated by pressurized air is considered in this book. Assuming that there exist uncertain parameters and uncertain external perturbations in the ship roll model, a backstepping structure with robust control algorithm for ship roll stabilization system is designed. A roll equation consisting of linear and nonlinear damping and restoring moment on the roll response is expressed. With the objective of reducing the number of required sensors, a model reference based nonlinear observer has been introduced. The control scheme provides a robust control system under parametric uncertainties and state variables estimation errors. The designed control implies an improvement on the conventional systems.