This report reviews the methods used to estimate the national number of people eligible to participate in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) under full funding of the program. It reviews alternative data sets and methods for estimating income eligibility, adjunctive eligibility (which occurs when people are eligible for WIC because they are enrolled in other federal public assistance programs) and nutritional risk, as well as for estimating participation if the program is fully funded.