Nearly 15 percent of all households and 39 percent of near-poor households were food insecure in 2008. The Supplemental Nutrition Assistance Program (SNAP, formerly called the Food Stamp Program) is the cornerstone of Federal food assistance programs and serves as the first line of defense against food-related hardship, such as food insecurity. This study measures SNAP's effectiveness in reducing food insecurity, using the 1996, 2001, and 2004 Survey of Income and Program Participation (SIPP) panels and a dummy endogenous variable model with instrumental variables to control for selection bias. The results suggest that receiving SNAP benefits reduces the likelihood of being food insecure by roughly 30 percent and the likelihood of being very food insecure by 20 percent. These findings provide evidence that SNAP is meeting its key goal of reducing food-related hardship. This study was conducted by The Urban Institute under a cooperative research contract with USDA’s Economic Research Service (ERS) Food and Nutrition Assistance Research Program (FANRP): contract number 59-5000-7-0113. (ERS project representative: Laura Tiehen). The views expressed are those of the authors and not necessarily those of ERS or USDA.