This essay is part of a larger project exploring the extent to which the market paradigm might be usefully employed to explain and in some instances justify nonmarket institutions. The focus of the market paradigm in this essay is the relationship between the idea of a perfectly competitive market and aspects of both the rationality of political association and the theory of collective choice. In particular, this essay seeks to identify what connections, if any, exist between one kind of market (...) account of the rationality of political association and one kind of market-based social choice rule. The market theory of political association I intend to discuss I call “market contractarianism,” and the collective choice rule whose relation to it I intend to explore is the unanimity rule. What, if anything, is the relationship between market contractarianism and the unanimity rule? (shrink)