1 in 7 Americans received assistance from SNAP in FY2012, which is a rate 141 percent higher than in FY2000, but only 59 percent higher than in FY1980. In this chapter I describe the socioeconomic and policy climate in recent decades that had bearing on SNAP participation, along with a formal empirical analysis of those determinants and detailed simulations of the relative contributions of the economy, policy, and demographics to changes in SNAP participation over time. The results suggest that SNAP is operating effectively as an automatic fiscal stabilizer—nearly 50 percent of the increase in participation from 2007–2011 is due to the weak economy—but policy reforms expanding access and benefit generosity also affected participation, accounting for nearly 30 percent of the increase after the Great Recession. The changing demographics of the American household are helping restrain growth in SNAP.