We describe the enormous changes in social and tax policy in recent years that have encouraged work by single mothers. We document the magnitude and timing of changes in federal and state income taxes, AFDC and Food Stamp benefits, Medicaid, and child care programs. We also describe how these changes differed across groups of states and different types of families. We then examine whether the changes in employment are consistent with a causal effect of these policies on employment, using multiple comparison groups and two datasets over a long time period. We find substantial evidence of large tax effects on employment.