Harmful alcohol use and sexually transmitted infections (STIs) are significant public health concerns for college students. Because alcohol use and condomless sex often co-occur in this population, alcohol-associated condomless sex has been identified as a target for behavioral interventions. Existing theoretical frameworks have not garnered sufficient empirical support to serve as the foundation for interventions. The primary goal of the current study was to use a mixed-methods approach to develop a novel model of college student alcohol-associated condomless sex that combines elements from well-established health behavior theories. In Aim 1, multilevel structural regression models were estimated to predict condomless vaginal intercourse in a sample of sexually-active college student drinkers (N = 57). An Exploratory Aim investigated the extent to which the model estimated in Aim 1 fit sexual activity occurring prior to the COVID-19 pandemic (N = 128). Aim 2 consisted of in-depth-interviews with a sub-sample of participants (n = 18) to gather perceptions about the role of alcohol in sexual activity and identify additional constructs pertaining to college student condom use. Quantitative results demonstrated the best-fitting model explained a significant proportion of variance in condomless vaginal intercourse at the between- and within-person level. Themes derived from the in-depth-interviews identified supplemental components of condom use decision-making. Findings from both aims were synthesized to construct a preliminary combined model of alcohol-associated condomless sex. This model can be refined in future work and ultimately serve as the theoretical foundation from which to develop a combination alcohol-STI prevention-intervention tailored to college students. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]