The topic of this paper is the foundation for individual rights proposed by David Gauthier in his seminal 1986 book Morals by Agreement, and particularly the role of conception of rationality in this foundation. The foundation of rights is a part of Gauthier’s broader enterprise: to ground morals in rationality – more specifically, in the economic conception of rationality. Because of the importance of this conception for the whole of Gauthier’s project, we reconstruct first the conception of rationality which can (...) be found in decision theory and game theory, presenting simultaneously in a relatively non-technical way some basic concepts of the aforementioned disciplines. We proceed then to reconstruction of the foundation of rights itself – it turns on Gauthier’s interpretation of the so-called “Lockean proviso.” Lastly, we turn to the connection between rationality and foundation of rights. It is to be found in the narrow compliance – the disposition to enter only into cooperation which satisfies conditions of fairness set out in part by the Lockean proviso. (shrink)