We argue that healthy people should be allowed to sell one of their kidneys while they are alive--that the current prohibition on payment for kidneys ought to be overturned. Our argument has three parts. First, we argue that the moral basis for the current policy on live kidney donations and on the sale of other kinds of tissue implies that we ought to legalize the sale of kidneys. Second, we address the objection that the sale of kidneys is intrinsically wrong because it violates the Kantian duty of respect for humanity. Third, we address a range of consequentialist objections based on the idea that kidney sales will be exploitative. Throughout the paper, we argue only that it ought to be legal for an individual to receive payment for a kidney. We do not argue that it ought to be legal for an individual to buy a kidney.