Entrepreneurship capital and economic performance, Regional Studies 38, 949-959. The neoclassical model of the production function, as applied by Solow when building the neoclassical model of growth, linked labour and capital to output. More recently, Romer and others have expanded the model to include measures of knowledge capital. This paper introduces a new factor, entrepreneurship capital, and links it to output in the context of a production function model. It explains what is meant by entrepreneurship capital and why it should influence economic output. A production function model including several different measures of entrepreneurship capital is then estimated for German regions. The results indicate that entrepreneurship capital is a significant and important factor shaping output and productivity. The results suggest a new direction for policy that focuses on instruments to enhance entrepreneurship capital.