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In 1974, Supplemental Security Income (SSI) federalized cash welfare programs for the aged, blind, and disabled, imposing a national minimum benefit. Because of pre-existing variation in generosity, SSI differentially raised payment levels in states below its benefit floor, but had no effect in states that paid above it. We show that SSI increased disability participation in states with the lowest pre-SSI benefits, but shrank non-disability cash transfer programs. For every four new SSI recipients, three came from other welfare programs. Each dollar of per capita SSI income increased total per capita transfer income by just over 50 cents.