This thesis considers a modelling and vibration analysis of thin spinning disks. Both in-plane and transverse vibrations are considered. Kirchhoff and von Karman theory of plates dong with Hamilton's principle are used to derive Iinear and nonlinear equations of motion for the vibrations of a spinning plate. In-plane and rotary inertias are naturally accounted for in this procedure. The resulting equations are similar to those previously derived in the literature but contain some additional terms. These linear and nonlinear equations are subsequently analyzed. New orthogonality properties of the in-plane modes are derived and are used to construct solutions to the linear, forced in-plane vibration problem. The linear transverse vibration equations are derived with new terms. These new terms are explained physicaily and their effect on the frequencies of vibrations is analyzed. Nonlinearly coupled transverse and in-plane vibrations are considered while including the effect of in-plane inertia which has dways been neglected by ot her researchers. It is found that the inclusion of in-plane inertia introduces the possibility of intemal resonance between the in-plane and transverse modes of vibration.