Despite the health benefits of participation, many eligible households do not participate in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC). While roughly half of infants born in the United States receive WIC benefits, USDA statistics indicate that eligible pregnant women and children 1-5 years of age are far less likely to participate in WIC than eligible infants and postpartum women. This implies that a number of pregnant women delay enrollment until after having a child, and that many households leave the program when a participating child turns 1 year old. Research on the factors that influence the dynamics of WIC participation can inform outreach and targeting efforts, so that vulnerable populations receive adequate exposure to the benefits of WIC participation.