Sustained growth in agricultural productivity is critical to improvements in food security for two reasons. First, growth in agricultural productivity translates into increased food supplies and lower food prices for consumers. And second, growth in agricultural productivity means higher incomes, and thus improved ability to purchase food and other basic necessities, for many food-insecure people who earn their livelihoods through agricultural production. Most changes in agricultural productivity over time (and differences across farms or countries) can be attributed to differences in the quantity of resources used in agricultural production, such as land, labor, and fertilizer.  But agricultural productivity also depends critically on the quality of resources used, including the quality of natural resources such as land. Distinguishing the relative impacts of resource quantity and quality is important in determining appropriate policy measures.