The Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) is an important source of nutritional support and education for women and children living in poverty; although WIC participation confers clear health benefits, only 50% of eligible women and children currently receive WIC. In 2010, Congress mandated that states transition WIC benefits by 2020 from paper vouchers to electronic benefits transfer (EBT) cards, which are more convenient to use, are potentially less stigmatizing, and may improve WIC participation. To estimate the state-level association between transition from paper vouchers to EBT and subsequent WIC participation. This economic evaluation of state-level WIC monthly benefit summary administrative data regarding participation between October 1, 2014, and November 30, 2019, compared states that did and did not implement WIC EBT during this time period. Difference-in-differences regression modeling allowed associations to vary by time since policy implementation and included stratified analyses for key subgroups (pregnant and postpartum women, infants younger than 1 year, and children aged 1-4 years). All models included dummy variables denoting state, year, and month as covariates. Data analyses were performed between March 1 and June 15, 2020. Statewide transition from WIC paper vouchers to WIC EBT cards, specified by month and year. Monthly number of state residents enrolled in WIC. A total of 36 states implemented WIC EBT before or during the study period. EBT and non-EBT states had similar baseline rates of poverty and food insecurity. Three years after statewide WIC EBT implementation, WIC participation increased by 7.78% (95% CI, 3.58%-12.15%) in exposed states compared with unexposed states. In stratified analyses, WIC participation increased by 7.22% among pregnant and postpartum women (95% CI, 2.54%-12.12%), 4.96% among infants younger than 1 year (95% CI, 0.95%-9.12%), and 9.12% among children aged 1 to 4 years (95% CI, 3.19%-15.39%; P for interaction = .20). Results were robust to adjustment for state unemployment and poverty rates, population, and Medicaid expansion status. In this study, the transition from paper vouchers to WIC EBT was associated with a significant and sustained increase in enrollment. Interventions that simplify the process of redeeming benefits may be critical for addressing low rates of enrollment in WIC and other government benefit programs.