The social discount rate – the rate at which future benefit flows from government investment are discounted to present value – has been a frequent subject of technical debate among professional economists. From a broader perspective, however, the selection of an appropriate rate enjoins consideration of questions that define the very contours of our public philosophy. It carries implicit assumptions about the nature of citizenship, the relation between public and private spheres, and, most singularly, the status of a political society as it is located in time. A key determinant of intertemporal economic allocation, the social discount rate provides a unique registry of a polity's historical consciousness and perceptions of its intergenerational obligations. Yet the highly technical nature of the debate over the discount rate has proven inhospitable to scholars otherwise inclined to investigate its ethical dimensions. Some, notably A. K. Sen, have begun to address these philosophical issues, though much territory remains to be explored.