Ronald Coase received the Nobel Prize in 1991 “for his discovery and clarification of the significance of transaction costs and property rights for the institutional structure and functioning of the economy.” Coase is an unusual economist for the twentieth century, and a highly unusual Nobel Prize winner. First, his writings are sparse. In a sixty-year career he wrote only about a dozen significant papers—and very few insignificant ones. Second, he uses little or no mathematics, disdaining what he calls “blackboard economics.” Yet his impact on economics has been profound. That impact stems almost entirely from two of his articles, one published when he was twenty-seven and the other published twenty-three years later.