Project Summary/Abstract Tobacco use, a primary behavioral risk factor for cancer, is the leading cause of preventable morbidity and mortality in the U.S. Adults with low socioeconomic status (SES) and members of certain racial/ethnic minority groups are less likely to quit and consequently experience profound tobacco-related cancer disparities. There is an urgent need to improve upon evidence-based smoking cessation interventions to better serve these populations. Mindfulness training substantially increases rates of smoking cessation and lapse recovery. There is a dearth of research on mindfulness in low-SES and racial/ethnic minority groups, but these interventions do show promise for smoking cessation in these populations. However, additional between-session support may be needed for these smokers, who experience significant day-to-day barriers to quitting and have lower access to smoking cessation resources. Mobile health technology (mHealth) could provide vital 24/7 support for low- SES smokers. For example, personalized, interactive mHealth messages might encourage participants to use mindfulness and other smoking cessation techniques in the moments when they need them most (e.g., in times of high stress or craving), thus enhancing treatment effectiveness. Based on iterative feedback from low- SES, racially/ethnically diverse smokers, we developed a text messaging program (“iQuit Mindfully”) as an adjunct to in-person mindfulness-based smoking cessation treatment. Our pilot work demonstrates that iQuit Mindfully is feasible, acceptable, and perhaps most effective for low-SES smokers (i.e., 23.1% of participants living in poverty who received iQuit Mindfully achieved abstinence at end of treatment and 1-month follow-up, while none of those living in poverty quit in the in-person-only treatment). Building on this pilot work, we will incorporate participant feedback to further increase interactivity and personalization so that iQuit Mindfully can more flexibly adapt to participants’ changing needs. The specific aims of this project are to: 1) Test the efficacy of a mindfulness-based smoking cessation intervention enhanced by mHealth (iQuit Mindfully), compared to in- person mindfulness-based addiction treatment (MBAT) and usual care; and 2) Investigate the mechanisms through which MBAT and iQuit Mindfully impact smoking cessation using intensive daily diary assessment. This project aims to improve cessation outcomes for low-SES, racially/ethnically diverse smokers by supplementing existing mindfulness treatment with innovative mHealth methods. Furthermore, we aim to advance the scientific study of mechanisms of action of mindfulness treatment, which could inform the development of more efficacious and efficient treatments to reduce tobacco-related cancer disparities.