This paper discusses the various aerodynamic considerations involved in tail rotor design. Sizing criteria are given, and the contribution of gyroscopic precession in causing blade stall during fast turns is explained. The stall boundaries for several Bell helicopters are shown as a function of yaw rate and acceleration. These acceleration and rate values are suggested as a minimum requirement for future designs. The effects of fin interference for both the tractor and pusher configurations are discussed and the apparent effects of direction of rotation are noted. Considerations are discussed which involve selecting a tail rotor's disc loading, tip speed, airfoil section, and design torque. Included are noise, efficiency, and structural loading. The directional contro1 requirements of a helicopter and simplified equations for yaw and gust sensitivity, and yam damping are discussed. Some of the directional control problems encountered by the industry are described along with steps taken to correct them.