Sloshing liquid fuel induces additional forces and moments which affect the performance. Vehicle dynamics coupled with liquid fuel slosh dynamics represents a broder class of underactuated systems. This coupled nonlinear system has been considered for the development of output feedback control using sliding modes. A sliding mode control (SMC) is one of the robust control approaches which yields robust performance against model inaccuracies and uncertainties. Design of SMC includes design of the hyperplane to yield the desired closed-loop performance and the controller synthesis to confine the states on the designed hyperplane. This book addresses novel approaches of designing the hyperplane together with the synthesis of the appropriate control law for the slosh problem in continuous and discrete both. Proposed state based control algorithms are extended for output feedback control using sliding mode high gain observer. Discrete sliding mode observer and a fast output feedback techniques are also illustrated for the development of discrete output feedback control. Experimental validation of few of the algorithms is also presented.