The helicopter represents a very complex system, which produces unique vibration problems. This high level of vibration experienced on the helicopter has been an unfortunate feature throughout its existence, and considerable efforts have been expended over many years to reduce vibration to levels typical of other forms of air transport. The work presented has been undertaken on a project in collaboration with Westland Helicopters Limited and aims to identify possible improvements to an existing control strategy which has already been concerned with minimising the structural vibration of a helicopter, and is achieved by measuring the vibration at a number of points on the fuselage using accelerometers. This information is processed by a multivariable control algorithm which calculates a set of control forces for a set of hydraulic actuators, located at strategic points in the structure. Vibration reductions result from the combination of the actuator control forces with those induced in the fuselage by the rotor.