AbstractPromises lie at the center of persons' moral experience of one another, and contracts lie at the center of their legal experience of one another. Many of the most important relationships in our moral and legal culture characteristically arise in connection with promises and contracts of some form or other: Persons' families are connected to marriage promises, their work is connected to employment contracts, and even their citizenship is connected (albeit metaphorically) to the social contract. In all these cases, and in myriad others, promises and contracts establish relations among the persons who engage them. But in spite of the obviously communal character of promise and contract, the most prominent accounts of these practices remain firmly individualistic, seeking to explain the obligations they involve in terms of one or another service that these practices render to the several parties who engage them. Some theories emphasize that promissory and contractual obligations increase the freedom of promisors, by enabling them to project their intentions into the future and rendering plans of action that require such precommitments available to them. Other theories emphasize that promissory and contractual obligations reflect concern for the reasonable expectations of promisees and the harms that promisees suffer when these expectations are disappointed. And, most prominently, yet other theories emphasize that promissory and contractual obligations promote the well-being of both promisees and promisors, by increasing the reliability of social coordination and promoting the efficient allocation of resources. These theories differ from one another in many ways, to be sure, and they often cast themselves as competitors. But they are of a piece insofar as they all seek the roots of the morality of promise and contract in properties of the several individual participants in such agreements.