Abstract of Proposed Research Project The proposed research aims to advance scientific knowledge on the dismantling of unhealthy sleep habits during the transition to adulthood. Dismantling unhealthy habits involves disrupting or reducing the automaticity of engaging in the unhealthy habitual behavior. Given the far-reaching consequences of unhealthy habits, the dearth of research on dismantling habits is surprising. The proposed research has a distinct focus from the “parent” R01 (R01HD071065), which is testing an intervention that draws on the science of habit formation to assist young adults (aged 18-30 years) who have sleep problems to build healthy sleep habits. In the R01, the young adults (N = 160) are randomly allocated to the HABITs intervention with (HABITs+Texts) or without (HABITs alone) a novel text messaging intervention that was derived based on learning theory. The proposed research supplement to promote diversity will extend the R01 by adding measures, procedures, and applying advanced statistical methods to understand the impact of the interventions on dismantling unhealthy sleep habits in 70 young adults who participate in the R01. The new measures will be added at pre-treatment, all nine weekly treatment sessions, at the post-treatment assessment and at the 6-month follow-up. The proposed research has two aims. Aim 1 is to compare whether treatment condition predicts (a) change and (b) rate of change in dismantling unhealthy sleep habits. The hypothesis is that change and the rate of change in dismantling unhealthy sleep habits will be greater and faster for HABITs+Texts, relative to HABITs alone. Aim 2 is to test whether the relationship between treatment condition and sleep health behavior at 6-month follow- up is mediated by automaticity of unhealthy sleep habits at post-treatment. The hypothesis is that HABITs+Texts will predict more change in sleep health behavior indirectly through greater dismantling of unhealthy sleep health habits, relative to HABITs alone. This research supplement to promote diversity will contribute to the science of behavior change by providing a deeper understanding of the dismantling of habits and will provide a unique window into whether the intervention tested in the R01 is sufficient for dismantling unhealthy habits. Furthermore, understanding the developmental impact of dismantling unhealthy sleep habits during the transition from adolescence to adulthood contributes to the National Institute of Child Health and Human Development Strategic Plan as it includes a focus on “developmental impact of sleep…and the opportunity to either prevent or mitigate poor outcomes.”