In this chapter, I present the second part of Rawls' argument: the reasoning that leads to adopting the two principles of justice as fairness and to rejecting the other alternatives, mainly the utility principle in its various forms. As important as the reasoning itself is its setting in an Original Position (OP hereafter) where the parties, placed behind a “veil of ignorance”, reflect on how best to distribute “primary goods” among the persons they represent, goods that are not simply welfare, but include wealth and income as well as the basic liberties and the social bases of self-respect (TJ: 54–5). How can such a constraint on information lead to rational and effective arguments? Many critics have argued that the theory of justice would be more convincing without the cumbersome device of the OP that hides and even undermines Rawls' deepcommitment, beyond the metaphor of the social contract, to public justification and the ideal of equal respect. Conversely, some, such as David Gauthier, have claimed that the OP fails to exploit fully the resources of rational choice theory for deriving principles of justice from principles of rationality. The aim of this chapter is to explain why, in spite of widespread criticisms, OP arguments still constitute the heart of the doctrine, even if they are complemented by independent arguments and have been of ten misunderstood.