PROJECT SUMMARY/ABSTRACT Since the introduction of e-cigarettes in the U.S. in 2007, there has been a dramatic increase in the prevalence of e-cigarette use among adolescents. These high prevalence rates have been driven, in part, by beliefs that e- cigarettes are less harmful than combustible cigarettes. Unfortunately, mounting evidence indicates that e- cigarettes pose significant health risks. E-cigarettes also contain nicotine, which can interfere with normal brain development. Because it is still developing, the adolescent brain is more vulnerable to the negative effects of nicotine exposure, putting adolescent e-cigarette users at greater risk of nicotine dependence as well as reduced impulse control and deficits in attention and cognition. Thus, although many had hoped that e- cigarettes would serve as a smoking cessation tool, they may, in fact, be ushering in a new generation of individuals dependent on nicotine. Therefore, we face an urgent need to promote e-cigarette cessation among adolescents. Unfortunately, the empirical literature on e-cigarettes has not been able to keep pace with their rapid increase in popularity. These knowledge gaps combined with the unique challenges of working with adolescent e-cigarette users have hindered the development of empirically supported e-cigarette cessation interventions for this population, and we currently lack targeted e-cigarette cessation interventions that are developmentally appropriate, grounded in empirically supported theories of behavior change, and acceptable to adolescents. To create such interventions, formative research is needed to better understand the different types of adolescent e-cigarette users based on their motivations for use rather than patterns of use. Identification of such a typology is critical as each type will have distinct cues, use patterns, beliefs, and preferences resulting in the need for type-specific interventions. Moreover, greater adolescent engagement is needed to ensure that the content of these interventions as well as the messaging surrounding them are acceptable to adolescents and take into account their perceptions of their own use. A mixed methods approach will be utilized to gather formative data on types of adolescent e-cigarette users and interventional targets specific to each type to inform the development of tailored cognitive behavioral e-cigarette cessation interventions for each type. A sample of 1200 high school students who have used an e-cigarette in the past month will be recruited. Self-report data will be used to identify e-cigarette user types based on motivations for use as well as cognitive and behavioral correlates of each type. Focus groups with users of each type as well as students who have successfully quit using e-cigarettes will provide further information about cognitive and behavioral intervention targets and cessation needs and preferences. The findings of this project will fill critical knowledge gaps that will result in...