Supplemental Security Income (SSI) is a needs-based financial assistance program "designed to help aged, blind, and disabled people . . . It provides cash to meet basic needs for food, clothing, and shelter." (Social Security Administration (SSA) website)
For the most part, SSI is governed by federal law and administered by a federal agency, SSA. The SSA is also principally responsible for administering other government benefits including social security disability insurance and social security (retirement).
The SSA Website offers information and materials on SSI including:
Medicaid is a health insurance and long-term care program primarily for low-income persons and, in some cases, for individuals with certain medical conditions. Medicaid is governed by a mixture of federal and state laws.
The CMS Website offers information and materials on Medicaid:
The Supplemental Nutrition Assistance Program (SNAP), formerly the food stamps program, is a need-based benefit that assists food purchases. SNAP is, for the most part, governed by federal laws but often administered on a state level.
The Department of Agriculture administers federal aspects of various nutrition assistance programs, including SNAP.
The Dept. of Agriculture Website offers information and materials on food programs: