The extent to which residents of the United States who are not U.S. citizens should be eligible for federally funded public aid has been a contentious issue for more than a decade. This issue meets at the intersection of two major policy areas: immigration policy and welfare policy. The eligibility of noncitizens for public assistance programs is based on a complex set of rules that are determined largely by the type of noncitizen in question and the nature of services being offered. Over the past 16 years, Congress has enacted significant changes in U.S. immigration policy and welfare policy. Congress has exercised oversight of revisions made by the 1996 welfare reform law (the Personal Responsibility and Work Opportunity Reconciliation Act, P.L. 104-193)-including the rules governing noncitizen eligibility for public assistance that it established-and legislation covering programs with major restrictions on noncitizens' eligibility (e.g., food stamps/SNAP, Medicaid). This report deals with the four major federal means-tested benefit programs: the Supplemental Nutrition Assistance Program (SNAP, formerly food stamps), the Supplemental Security Income (SSI) program, Temporary Assistance for Needy Families (TANF) block grant programs, and Medicaid. Laws in place for the past 15 years restrict the eligibility of legal permanent residents (LPRs), refugees, asylees, and other noncitizens for most means-tested public aid. Noncitizens' eligibility for major federal means-tested benefits largely depends on their immigration status; whether they arrived (or were on a program's rolls) before August 22, 1996, the enactment date of P.L. 104-193; and how long they have lived and worked in the United States. LPRs with a substantial work history or military connection are eligible for the full range of programs, as are asylees, refugees, and other humanitarian cases (for at least five to seven years after entry). Other LPRs must meet additional eligibility requirements. For SNAP, they generally must have been legally resident for five years or be under age 18. Under TANF and SSI, they generally are ineligible for five years after entry and then eligible at state option. States have the option of providing Medicaid to pregnant LPRs and children within the five-year bar. Unauthorized aliens (often referred to as illegal aliens) are not eligible for most federal benefits, regardless of whether they are means tested, with notable exceptions for emergency services, (e.g., Medicaid emergency medical care or Federal Emergency Management Agency disaster services). TANF, SSI, food stamp, and Medicaid recipiency among noncitizens decreased over the 1995-2005 period, but has inched upwards in 2011. While the 10-year decrease was affected by the statutory changes, the poverty rate of noncitizens had also diminished over the 1995-2005 decade. The poverty rate for noncitizens residing in the United States fell from 27.8% in 1995 to 20.4% in 2005. It has risen to 24.3% in 2011. Noncitizens are disproportionately poorer than native-born residents of the United States.