Incentives that reward healthier food purchases and that provide reinforcement to the consumer have not been systematically and rigorously studied, particularly among lower-income populations. The aim of this study is to determine whether an incentive-based system increases healthier food purchasing practices by lower-income families. The study is a randomized controlled trial of 70 adult supermarket shoppers in Northwest Philadelphia who have at least one child 5 to 16 years of age living in the home. Participants randomized to the incentive arm have the opportunity to accumulate market dollars for a supermarket-based gift card, based on their purchases of fruits and vegetables. There are four phases of the study: 1) 8-week baseline purchase history; 2) 8-week active intervention; 3) 6-week tapering of the intervention; and (4) 6-week follow-up. Electronic supermarket data will be collected via frequent shopper cards, and participants will be interviewed at the beginning and the end of the study. This study will yield important data for community and policy stakeholders about the use of this form of incentive and its potential to increase healthier food purchasing practices in lower-income households.