Project Summary States have responded to the emergence of electronic nicotine delivery systems (ENDS) through implementing several types of policies specific to ENDS in addition to existing tobacco control policies. At present, the full efficacy of both types of policies on ENDS and related tobacco use among adolescents is unknown. This research study will use multiple, complementary statistical methods and a robust policy database to examine the impact of relevant tobacco and ENDS-specific policies on ENDS use and related tobacco use among adolescents. We will merge tobacco policy and ENDS-specific policy data from the American Nonsmokers’ Rights Foundation (ANRF) to evaluate the effects of these policies on patterns of adolescent ENDS and related tobacco use (initiation, prevalence, duration, frequency, and cessation). We will accomplish this goal by coding this policy database by state and year and combining it with data from the Population Assessment of Tobacco and Health (PATH) and key time-varying measures from the U.S. Census. In our first pair of aims, we will analyze this data using mixed effects models, using both within- and between-person effects. Respectively, these two types of effects determine (a) whether adolescents change their ENDS and tobacco use after their state of residence passes a particular policy, and (b) whether adolescents in a state that passes a policy experience significantly different trajectories of ENDS and tobacco use relative to those in a state without the policy. In addition, we will introduce sequence analysis, which allows for a more detailed depiction of transitions into and out of ENDS and related tobacco use, and testing of differences in trajectories across policies. We also will test for synergistic effects of policy; that is, whether the combination of any given policies is particularly effective. In our second pair of aims, we assess policy effect differences across particular respondent characteristics. First, we will consider whether parent contexts moderate the effects of policies. Finally, we will conduct analyses of policy effects by key demographics: socioeconomic status, gender, race/ethnicity, and rural/urban locale, which will permit the identification of related health disparities. Our proposed research provides opportunities to test the impact of a rapidly evolving policy landscape on ENDS outcomes and will contribute in the following ways. First, if certain policies or combinations of policies are identified as efficacious, the results would provide evidence for broader adoption to curb current ENDS trends. Second, the identification of possible health disparities in the benefits of policy implementation may not only help health professionals work towards redressing disparities, but also identify policies that may “bypass” social inequalities to provide comprehensive benefits to adolescents with long-term implications. Finally, this study establishes a foundation for future research that...