SFDs are widely used in rotating machinery to provide damping in order to control rotordynamic response. Although popular, under certain conditions SFDs pose problems such as causing non-synchronous vibration arising from unbalance forces interacting with fluid-film forces affected by cavitation. Furthermore, in the interests of moving towards oil-free rotating machines, the need arises to find alternative means of rotordynamic response control.In choosing a new vibration control technology, it is first necessary to consider certain general, configuration-independent criteria. For example, does the actuation method provide a limited stroke (eg. piezoelectric or giant magnetostrictive) or is the stroke a "motorised" solution (eg. an ultrasonic motor directly driving the actuator or a pump acting to vary the fill level of closed deformable volumes with incompressible fluid) Is the work per stroke per unit mass of the actuator material sufficient to provide the maximum stroke and force required for the control? What is the bandwidth of the actuator? In the case of electromechanical actuation, what is the coupling factor? Can the elements of the actuator withstand the high temperatures of the operating environment? Is the solution an active or passive one? What are the fatigue properties of the materials used in the actuator? These are some of the questions that need to be considered when evaluating a new control method.Once the significant properties have been identified, it is necessary to consider each of these in the context of the intended application. If one considers the actuation type, in the limited stroke case it will be required for the actuation to take place at synchronous frequency and the work per stroke per unit mass will determine the quantity of material required. For some applications – particularly aero-engines – one seeks to minimise overall mass and therefore materials with high values of work per stroke per unit mass are attractive. By contrast, in the case of motorised solutions the frequency of operation of the actuator may be orders of magnitude greater than synchronous speed. Since the main source of rotordynamic vibration arises from rotor unbalance – which causes vibration at synchronous speed – the control is also required (at least) at synchronous speed. Therefore, the actuation method should have a bandwidth equal at least to this speed. The coupling factor for piezoelectric and magnetostrictive actuators will determine the amount of energy that should be supplied for a given requirement of work, and therefore high values of this property are desirable. Whether the vibration control method is active or passive will also influence the overall weight and complexity of the machine.Damping is not the only method by which vibration may be controlled. For example, if it is possible to alter the natural frequencies of the rotor-stator system as the system is approaching a resonance, then the build up of substantial vibration can be avoided as the system effectively never sits on a resonance.In the present work, various actuation technologies such as piezoelectric, magneto-strictive, electromagnetic, shape memory alloys and ultrasonic motors have been considered. Some of these technologies are considered in more detail as they show more potential of being implemented in a relatively uncomplicated configuration, in the intended application.