The Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) provides supplemental food, nutrition education (including breastfeeding promotion and support), and referrals to health care and other social services to low-income, nutritionally at-risk women, infants, and children up to 5 years of age. On average, over half of all infants in the United States, over a quarter of all pregnant and postpartum women, and over a quarter of all children less than 5 years of age participate in the program. The Healthy, Hunger-Free Kids Act of 2010, which authorized funds for WIC, is set to expire on September 30, 2015. The reauthorization process provides an important opportunity to reexamine the operation and effectiveness of the program and to consider improvements. This report explains how WIC works, examines program trends, and discusses some of the major economic issues facing the program (including the impact of economic conditions on participation, some lesser known effects of WIC, and equity and cost-management issues).