The reduction of helicopter vibration Is of great Importance to the helicopter Industry and considerable effort has been devoted to research into active methods for vibration reduction. This article describes how active control techniques can offer good vibration reduction over significant areas of the fuselage and also provide the capability to adapt to changing speed, rotor conditions and structural dynamics. There are three main areas on the helicopter where active vibration control techniques can be applied: at the rotor, at the main gearbox to fuselage interface, and within the fuselage itself. The last area is termed the active control of structural response (ACSR) and is considered In more detail. Finally, the performance of the ACSR technique in minimising vibration in helicopter structures Is analysed using results which demonstrate the performance potential under differing conditions.