The Food Stamp Program (FSP) helps low-income individuals purchase food so that they can obtain a nutritious diet. One important measure of a program’s performance is its ability to reach its target population, as indicated by the fraction of people eligible for benefits who actually participate. Of the 38 million individuals who were eligible for food stamp benefits in an average month of 2004, 23 million individuals (60.5 percent) chose to participate. There were over 15 million eligible individuals who did not participate in 2004. Although the FSP served more than 60 percent of all eligible individuals, it provided over two-thirds (70.6 percent) of the benefits that all eligible individuals could receive. This is because the neediest individuals, who are eligible for higher benefits, participated at higher rates than other eligible individuals. The rate of participation by demographic and economic subgroups continued to follow historical patterns in 2004. Rates were relatively high for individuals in households below the poverty line, in households with children, and for recipients of Temporary Assistance for Needy Families (TANF) or Supplemental Security Income (SSI), with at least three-quarters of all eligibles from these groups participating. On the other hand, less than a third of eligible elderly adults, nondisabled childless adults, and individuals living in households with incomes above the poverty line, and only slightly more eligible noncitizens, participated in the FSP in 2004. Participation rates for eligible individuals in households with earnings and citizen children living with noncitizens were also lower than average, just over 50 percent. Nationally, the participation rate among individuals increased by just under 5 percentage points between 2003 and 2004, the third annual increase after declining for 7 years. Almost every demographic and economic subgroup experienced a rise in participation rates, with particularly large increases in the participation rate of children, of individuals in households with very low income, and of individuals receiving the maximum benefit.