The present invention relates to wind turbines and more particularly to a multi-element airfoil for a vertical or horizontal axis wind turbine. In one embodiment, a vertical wind turbine includes a plurality of blades arranged in an annular path around a central axis of rotation. Each blade includes a first element and a second element that are nestable together. The first element has a concave rear surface, and the second element has a convex leading surface. Each of at least 45% of the blades generates a lift in a direction of rotation of the turbine that is greater than a drag generated by the same blade.