Reward & Reminder, a population-level intervention targeting whole communities, counties, or States, is designed to promote the community norm of not selling tobacco to minors. By using rapid and public rewards and recognition for clerks and retailers/outlets that do not sell tobacco to minors, Reward & Reminder aims to reduce illegal sales of tobacco, perceived access to tobacco, and tobacco use prevalence rates. The intervention emerged from a contextual analysis of factors affecting the behavior of store clerks, retailers, and the tobacco industry overall. At the core of the program is the use of “mystery shoppers,” teams of youth who–with parental permission and under the supervision of adults–enter stores and try to buy tobacco products. They provide immediate recognition and rewards, such as gift certificates, to clerks who do the “right thing” and give reminders to those who do not. The results of the mystery shopper visits are entered into a Web-based system where they are made publicly visible, and the results are communicated to local media to promote the positive norm. The mystery shopper visits are scheduled across the year to maximize the immediate and sustained impact. Using on-site or Web-based training, community adults who pass background checks can be trained as supervisors in about 3 hours, and approved youth can be trained as shoppers in about an hour. Quality control is maintained using a Web-based data entry system that facilitates data collection and guides implementation and fidelity activities.