Project Summary The long-term objective of the proposed study is to determine whether simultaneous alcohol and marijuana use temporally precedes and increases the risk for high-risk sexual behavior, and whether distal impulsivity and simultaneous alcohol and marijuana peer norms moderate this temporal association in college students. The proposed study will utilize daily diary methodology to examine the aims and hypotheses. High-risk sexual behaviors are associated with a variety of negative outcomes (e.g., unwanted pregnancies) and are incredibly prevalent in young adult populations, as are rates of alcohol and marijuana use. The proposed study aims to investigate the relationship between simultaneous alcohol and marijuana use and high-risk sexual behaviors in 100 alcohol and marijuana-using, sexually active college students. To date, no research exists that has examined the temporal relationship between simultaneous alcohol and marijuana use and high-risk sexual behaviors in college students. In the proposed study, participants will complete 30 days of daily diaries reporting on their alcohol use, marijuana use, and high-risk sexual behaviors. This methodology will allow for accurate elucidation of this temporal relationship. This project can provide critical information for future interventions aimed at reducing high-risk sexual behaviors in college students.