Owing to its excellent vibration isolation capability, the squeeze film damper is finding increasing use in industry, particularly in the gas turbine industry. Design information for squeeze film damper supported flexible rotors has been scarce and has been restricted mainly to small journal orbit eccentricity, and consequently to small unbalance loading. However, unbalance loading can increase in service, resulting in highly undesirable operation modes. This thesis analyses theoretically and experimentally the effect of the relevant system parameters on the possibility of such undesirable operation modes, on unbalance force transmissibilities, on rotor excursion amplitudes and on the orbit stability of squeeze film damper supported flexible rotors, with a view to aid the design of such rotor bearing systems. Assuming Reynolds equation with constant lubricant properties, the short bearing approximation and synchronous symmetric motions, the equations of motion are solved numerically. Rotor excursion amplitude and transmissibility data are presented for a wide range of operating conditions, showing the effect of the system parameters on the responses. It is shown that pressurization of the oil supply is conducive to smooth passage through the first pin-pin critical speed of the rotor. The system stability is investigated for small perturbations from the equilibrium solution (using Routh's criterion) and stability maps are superimposed on the journal eccentricity frequency response plots). Pressurization is shown to stabilize the rotor bearing system and supply pressure data are presented, showing the minimum pressure required to suppress the undesirable operation mode and to ensure stable operation. A theoretical model is developed for optimal fine tuned system design. Optimal support data and the system responses are presented on a single chart for a wide variety of rotors operating under the second bending critical speed. The design and commissioning of the experimental rig and the subsequent experimental investigation to verify the theoretical findings are described in detail. Very good agreement is obtained between theoretical predictions and experimental results. It is concluded that the theoretical model and predictions are valid.