The growth of the national debt, which is considered unsustainable under current policies, continues to be one of the central issues of domestic federal policymaking. Addressing a federal budget deficit that is unsustainable over the long run involves choices. Fundamentally, the issues require deciding what government goods, services, and transfers are worth paying taxes for. Most people would agree that the country benefits from a wide range of government services-air traffic controllers, border security, courts and corrections, and so forth-provided by the federal government. Yet federal government provision of goods and services comprises only a modest portion of the federal budget. Transfers, including interest payments, accounted for around 75% of the federal budget. Central findings of this analysis include the following: A comparatively small share of federal spending is for the direct provision of domestic government goods and services. Transfers and payments to persons and to state and local governments constitute most of federal spending, about 75% of all federal spending. Defense spending, accounting for about 15% of federal spending, has declined as a share of output over the past 35 years, but it also tends to vary depending, in part, on the presence and magnitude of international conflicts. The problem with the debt lies not in the past but in the future, as growth in spending for health and Social Security is projected to continue faster than the economy as a whole. The increase in deficits and debt, in turn, leads to a significant increase in interest payments. Because much of the pressure on future spending arises from imbalances in Social Security and Medicare Part A (Hospital Insurance) trust funds, keeping these funds and their sources of financing intact is a concern that could constrain choices. Preserving entitlements would likely require significant increases in taxes, such as raising rates, reducing tax expenditures, increasing other taxes, or introducing new revenue sources. Reductions in discretionary spending are insufficient to reduce the deficit to a sustainable level, so limiting taxes as a percentage of output or constraining the overall size of the government to current levels would likely require significant cuts in mandatory spending, including entitlement programs such as Social Security, Medicare, and Medicaid. Because the federal government provides about one-fifth of the revenue for state and local governments, cutbacks in transfers to these governments may, in part, shift the burden of providing services from the national to subnational governments rather than altering the overall size of government services.