For most, food is consumed several times a day. Although familiar, food is in no way an ordinary item of consumption. Food dominates the budget of the poor, but decreases in relative importance as increase rises, a strong empirical regularity called Engel’s law, considered one of the most fundament “laws” of economics. Additionally, relative to the poor, more affluent consumers have more diversified diets, reflecting higher quality. Using the economic approach to food consumption, this chapter deals with the foundations and implications of Engel’s law, the income and price elasticities of food demand, the measurement of diet diversity, and the quality of eating patterns across the income distribution.