The work of the early pioneers which led to the evolution of the current helicopter configurations is briefly reviewed. The major mechanical elements of the helicopter are then identified: the engine, transmission and blades analogous to the engine, transmission and wheels of a road vehicle. The paper then briefly reviews the design problems and the state of the art in helicopter engines, gearboxes, rotor blades and hubs, rotor controls and the important resonant and unstable conditions of the total system which must be avoided. Methods for ground testing the elements of the dynamic system are then presented. The paper concludes with a brief account of health and usage monitoring which will play an increasingly important part in improving reliability and reducing operating cost.