This paper discusses the various aerodynamic and dynamic con-siderations involved in the design of the rotor system of single-rotor helicopters. Design parameters of a helicopter rotor and their influence on the rotor thrust efficiency, stall behaviour, helicopter flying qualities, vibration and noise at different flight modes are well defined. Some of these parameters: have contradictory effects on the rotor flight characteristics. Others are either strictly related together, or cannot be arbitrarily varied because of structural, me-chanical and aerodynamic limitations. Necessary compromises should then be made in order to come up with the optimum design of the rotor system. A definite procedure for optimizing values of these parameters to give the best flight characteristics of the helicopter concerning performance, stability, control, vibration and noise at different flight modes and user's requirements is clearly submitted by the author. This will be of great value to helicopter designers, both in modifying existing helicopters and designing new ones.