The Food Stamp Program (FSP) is intended to help low-income households afford a nutritionally adequate diet. Since 1990, the FSP caseload has varied widely-rising sharply in the early 1990s, dropping sharply in the late 1990s, and then rising again in the early 2000s. Welfare and food stamp policy changes, as well as the changing economic climate, are plausible candidates for explaining the path of the caseload over time. The authors estimate the effect of these three factors on the total caseload and on two of its components: persons in households combining cash assistance with food stamps, and persons in households where some or all are not receiving cash assistance. They find that together welfare reform and the improving economy explain all of the FSP caseload decline during the late 1990s, and that policies aimed at increasing access to the FSP and the weakening economy explain about half of the FSP caseload increase in the early 2000s. Results analyzing the disaggregated caseloads are not as clear-cut, apparently because of measurement issues during the period when Temporary Assistance for Needy Families (TANF) programs were implemented.