PROJECT SUMMARY Electronic cigarette (ECIG) use has become a popular method for nicotine delivery. Combustible cigarette (CC) cessation or reduction are the primary reasons for ECIG uptake among adults.1-3 Yet, most CC smokers who initiate ECIG use do not fully transition from CC to ECIG, despite intending to quit CC completely.4-9 Longitudinal work has found that 89% of dual users—users of ECIG and CC concurrently--remain dual users a year after initial assessment.10 Theory and empirical findings suggest that targeting automated, impulsive, implicit processes may hold promise for substance use reduction and cessation.11-16 Specifically, retraining approach bias, or the approach action tendency toward stimuli related to the substance of interest, has been effective in alcohol use disorders (i.e., reduction in relapse rates by 10%-13%).16-18 When applied to CC-related stimuli, approach bias retraining has been found to reduce approach bias, which is subsequently related to greater number of days abstinent from CC following a self-guided quit attempt.19 The parent grant will evaluate the initial efficacy of approach bias retraining among dual CC/ECIG users as well as putative mechanisms of treatment effects. In addition, the current supplement research project proposes to test clinically-relevant sociodemographic moderators (i.e., sex, race, and nicotine dependence [CC dependence and ECIG dependence separately]) of treatment effects and mechanisms. We will randomly assign 90 dual CC/ECIG using adults to one of three conditions: (1) CC+ECIG retraining; (2) CC only retraining; and (3) sham training (control). Participants will complete 4 sessions of approach bias retraining using the respective stimuli and then engage in a self-guided quit attempt to abstain from all nicotine products. Each session will consist of 15 minutes of computerized approach bias retraining and a brief assessment. Participants will provide baseline data, ecological momentary assessment (EMA) data during the first two weeks post-intervention, and complete follow-ups at 4- and 6-weeks post-intervention. Abstinence will be assessed during the intervention (weeks 0-4), during the EMA period, and at both follow-ups. Upon completion of data collection, we will run tests of moderation exploring sex, race, and nicotine dependence (CC and ECIG dependence separately) as independent moderators of treatment effects for point-prevalence abstinence, prolonged abstinence, and putative mediational pathways. This work is key to identify individual differences that may affect the efficacy of the intervention and its mediational pathways. The proposed supplement represents a crucial and important ‘next step’ in translating basic research strategies for treating nicotine dependence among dual CC/ECIG users. It will yield important findings to help us evaluate whether approach bias retraining interventions administered to dual users have a differential impact by sex, race, and perhaps nicotine...