A crucial factor in economic growth - the supply of entrepreneurship - is largely neglected in modern economic theory. The main reason is that the theory is dominated by the model of perfect competition, which logically excludes any function for the entrepreneur. The standard model is also inconsistent with several obvious facts. Instead, the author proposes two alternative models of 'entrepreneurial competition', one for conditions of near-perfect competition in product markets and the other for imperfect competition in those markets.