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The simplicity of the Variable Geometry Vertical Axis Windmill (VGVAW) makes it attractive for many applications, large scale and small. This paper concentrates on measurements that have been made at Reading University on the 3 m dia VGVAW prototype. Work on large scale versions of the design is proceeding separately in collaboration with industry. The performance of the 3 m, low solidity, prototype has been measured in the open air, and a peak power coefficient of 0.30 to 0.35 recorded. This is in reasonable agreement with theoretical predictions and compares favourably with available open-air test data for Darrieus and horizontal axis windmills. The choice of optimum solidity is discussed in some detail, and the effects of low aspects ratio considered. It is shown that low aspect ratio combined with high solidity can be expected to give aerodynamic self start with only minor loss of performance. A low aspect ratio, high solidity vertical axis windmill was therefore also constructed, and these expectations confirmed. (Wassmann)