Social Security Disability Insurance (SSDI) applications and receipts vary greatly by state. This paper investigates the extent to which this geographic variation in SSDI applications reflects differences in health, demographics, and employment characteristics, state policies, and politics. We find that demographic, health, and employment characteristics of the state have the greatest effect on state-level variations in SSDI application rates, explaining over 70 percent of the variation. State policy concerning mandated employer-sponsored disability insurance (also known as temporary disability insurance or TDI) has a small negative effect on overall SSDI applications. This finding supports the principle underlying many recent SSDI reform plans: temporary disability insurance coverage could save the SSDI program considerable funds in the long run. Further, when we look to explain variation within a state, we find that state changes in health insurance regulation are negatively correlated with the SSDI application rate. This could be an indication that the Affordable Care Act (ACA) may have spillovers to the SSDI program.