The augmented vertical axis wind turbine resulted from a survey of the problems of existing wind turbines, and the identification of the design criteria that it should be inherently safe and reliable. It should be self-starting in low winds and continue to run in high Winds, and it should be environmentally acceptable. The design consisted of a vertical axis rotor, with five vertical and five horizontal blades, surrounded by an augmentor which contained eight converging stators and a dome desigried to increase the flow rate through the rotor, and to decrease the pressure at exit from the rotor. Extensive model tests showed that the wind turbine had attractive operating characteristics, which were confirmed by a prototype machine with a 6m diameter rotor rated at 10kW. However, a detailed analysis of the design and costs showed that it was too expensive. An analysis of an idealised augmented vertical axis wind turbine showed that there was potential for increasing the performance and decreasing costs. Measurements of the detailed flow field through the rotor and around the augmentor demonstrated that augmentation was by means of an increased pressure drop across the rotor, combined with an increased mass flow rate through it. The efficiency of the upstream part of the rotor was also increased by the augmentor. The benefits of turbulent mixing in the wake of the turbine between the external flowfield and the flow through the turbine were also recognised. Major modifications to the design of the augmentor and rotor resulted in two types of wind turbine which maintained the attractive operating characteristics and appeared to be commercially viable. The designs offer particular benefits in terms of inherent safety and reliability. The potential of cost effective, large multi¬megawatt machines is also recognised. The work has also provided further insight into wind turbine augmentation, and in the design and development of vertical axis rotors.