PROJECT SUMMARY / ABSTRACT Heavy alcohol use is prevalent in the United States and results in significant physical and psychological burden. One in 10 adults in the United States reports binge drinking on a weekly basis, and few are willing to seek mental health treatment. Thus, additional strategies are needed to engage and treat individuals at risk for alcohol-related harm. Half of those who screen positive for hazardous drinking report clinically significant symptoms of insomnia. Insomnia tends to be less stigmatized than other mental health disorders, and it is one condition for which we have highly efficacious treatment. Thus, one potential strategy to engage individuals in mental health treatment and reduce the burden of alcohol use in the United States is to target insomnia. The proposed five-year R01 aims (1) to investigate daily associations between sleep and alcohol use, (2) to examine change in insomnia as a mediator of CBT-I effects on alcohol use outcomes and sex as a moderator of those effects, (3) to identify mechanisms linking change in insomnia to alcohol use outcomes, and (4) to evaluate CBT-I effects on cardiovascular outcomes. Heavy-drinking adults with insomnia will be randomly assigned to Cognitive Behavioral Therapy for Insomnia (CBT-I, n=112) or waitlist control (WLC, n=112). Outcomes will be assessed mid-treatment (after 3 sessions), at the end of the active intervention period (post- treatment), and at 1, 3, and 6 month follow-ups. Primary outcomes include insomnia severity, drinking quantity, and alcohol-related consequences. Data will be analyzed using multilevel models. The results of the proposed research will inform research and clinical practice by determining the extent to which sleep operates as a mechanism of alcohol behavior change. Its innovation lies in evaluation of insomnia not only as a gateway to mental health treatment, but also as a mechanism of improvement in alcohol-related consequences. This is consistent with NIAAA’s strategic plan to evaluate interventions that target sleep.