PROJECT SUMMARY. Massachusettsis the first state inthe nation to restrict retail sales of all flavored tobacco products including e-cigarettes, combustible and smokeless tobacco to 21-and over smoke shops. The new MA law presents a time-limited opportunity to obtain baseline information on the initial impacts of the law on youth and adults' tobacco use and adults' quit attempts following the law's implementation. It is also critical to examine barriers and facilitators of implementing the law's provisions across the state during this initial period. Knowledge gained from this research would provide much needed and time-sensitive evidence to inform other states on the benefits or unintended effects of additional restrictions. Our long-term goals are to prevent all forms of tobacco product use among youth and assist youth and adult tobacco users with evidence- based cessation treatments. The objectives of this study are to estimate the initial impacts of the new MA law on tobacco use behaviors among youth and adults and quit attempts among adults in MA compared with four adjacent New England states and to identify the barriers and facilitators during the initial period of implementing the MA law. Our scientific rationale is based on the Integrated Implementation and Mediation Model of Tobacco Control Policy. We will obtain pre-law data of tobacco use and quit attempts (2019 Youth Risk Behavioral Survey and Behavioral Risk Factor Surveillance System) and collect post-law data through monthly repeated cross-sectional online surveys among youth ages 13-17 (n=1800) and adult current tobacco users ages 18+ (n=1800). Using a quasi-experimental design, we will perform propensity score difference-in- differences (DID) analyses to estimate changes in the study outcomes pre- and post-law among participants in MA and 4 control states (NH, VT, RI, and CT). We will examine the post-law monthly trends in study outcomes in MA and 4 control states. We will conduct key informant interviews with 32 stakeholders in MA (school district superintendents, principals, health providers, health department officials, tobacco retailers) to assess facilitators and barriers of implementing the new law. Our specific aims are: 1) Estimate the pre- and post-law changes in youth and adult use of tobacco products and adult quit attempts in MA compared with 4 control states (NH, VT, RI, and CT), 2) Examine the post-law trends in youth and adult use of tobacco products and adult quit attempts in MA and 4 control states (NH, VT, RI, and CT), 3) Identify policy implementation facilitators and barriers among key stakeholders in MA. Impact: This study will provide time-sensitive data to evaluate the initial impacts of the new MA law on tobacco use and quit attempts compared with less restrictive policies in control states in New England. The study findings will aid in implementing evidence-informed tobacco control regulations in states to prevent youth tobacco use and reduce the populatio...