T he propositions that organization matters and that it is susceptible to analysis were long greeted by skepticism by economists. To be sure, there were conspicuous exceptions: Alfred Marshall in Industry and Trade (1932), Joseph Schumpeter in Capitalism, Socialism, and Democracy (1942) and Friedrich Hayek (1945 in his writings on knowledge. Institutional economists like Thorstein Veblen (1904), John R. Commons (1934) and Ronald Coase (1937) and organization theorists like Robert Michels (1915 [1962]), Chester Barnard (1938), Herbert Simon (1957a), James March (March and Simon, 1958) and Richard Scott (1992) also made the case that organization deserves greater prominence.One reason why this message took a long time to register is that it is much easier to say that organization matters than it is to show how and why.1 The prevalence of the science of choice approach to economics has also been an obstacle. As developed herein, the lessons of organization theory for economics are both different and more consequential when examined through the lens of contract. This paper examines economic organization from a science of contract perspective, with special emphasis on the theory of the firm.1 A Behavioral Theory of the Firm (Cyert and March, 1963) was one obvious early candidate for an economic theory of organizations. It deals, however, with more fine-grained phenomena-such as predicting department store prices to the penny-than were of interest to most economists. For a discussion, see Williamson (1999b). The recent and growing interest in behavioral economics-which deals more with the theory of consumer behavior than with the theory of the firm-can be interpreted as a delayed response to the lessons of the "Carnegie school" associated with Cyert, March and Simon.