Social Security, in the United States, currently refers to the Federal Old-Age, Survivors, and Disability Insurance (OASDI) program.

The original Social Security Act and the current version of the Act, as amended encompass several social welfare or social insurance programs. The larger and better known initiatives of the program are:

• Federal Old-Age, Survivors, and Disability Insurance
• Unemployment Insurance
• Temporary Assistance to Needy Families
• Health Insurance for Aged and Disabled (Medicare)
• Grants to States for Medical Assistance Programs (Medicaid)
• State Children's Health Insurance Program (SCHIP)
• Supplemental Security Income (SSI)

Social Security in the United States is a social insurance program funded through dedicated payroll taxes called Federal Insurance Contributions Act (FICA). Tax deposits are formally entrusted to Federal Old-Age and Survivors Insurance Trust Fund, or Federal Disability Insurance Trust Fund, Federal Hospital Insurance Trust Fund or the Federal Supplementary Medical Insurance Trust Fund. The main part of the program is sometimes abbreviated OASDI (Old Age, Survivors, and Disability Insurance) or RSDI (Retirement, Survivors, and Disability Insurance). When initially signed into law by President Franklin Roosevelt in 1935, the term Social Security covered unemployment insurance as well. The term, in everyday speech, is used only to refer to the benefits for retirement, disability, survivorship, and death, which are the four main benefits provided by traditional private-sector pension plans. In 2004 the U.S. Social Security system paid out almost $500 billion in benefits. By dollars paid, the U.S. Social Security program is the largest government program in the world and the single greatest expense in the federal budget, with 20.9% for social security and 20.4% for Medicare The Social Security Administration is headquartered in Woodlawn, Maryland just to the west of Baltimore.

Largely because of solvency questions ranging from immediate crisis to large projected future shortfalls, reform of the Social Security system has been a major political issue for more than three decades during the presidencies of Gerald Ford, Jimmy Carter, Ronald Reagan, George H. W. Bush, Bill Clinton, and George W. Bush. (See Social Security debate (United States).)