ABSTRACT Alcohol use across the life course peaks for most individuals in young adulthood, and use during this developmental period is associated with numerous consequences and societal costs. Young adult alcohol use is a serious public health burden when considering the way in which young adults often drink; that is, young adults are more likely than individuals of other age groups to engage in binge drinking (five or more drinks in a row) and extreme binge drinking (ten or more drinks in a row). With emerging technology, we can now deliver mobile interventions to young adults before or during an actual drinking episode with the intent of reducing the overall amount of alcohol consumed in that episode and reducing negative consequences. However, there is a gap between theory, research, and the development of real-time interventions to the extent that theories rarely predict when an intervention might be most effective or how alcohol itself may influence specific risk factors. The proposed research aims to address this gap by measuring alcohol expectancies and their salience (i.e., the amount of attention paid to specific potential alcohol-related outcomes) in young adults’ natural environments, examining the extent to which expectancies and their salience shift in response to alcohol consumption and across real-world contextual factors, and examining whether these shifts are associated with subsequent alcohol consumption. To do so, the research utilizes ecological momentary assessment (EMA) methodologies: 240 young adult heavy drinkers will complete a 24-day EMA study spanning across four weekends, and will self-report alcohol expectancies and their salience at the daily level and before and during drink episodes in the natural environment. EMA will maximize ecological validity and allow for examination of how alcohol expectancies and their salience shift as a function of alcohol consumption itself as well as real- world contextual factors. We will also assess alcohol’s acute effects as reported during drinking occasions and examine whether these effects are associated with alcohol expectancies and their salience. Finally, examination of person-level moderators will allow for identification of who may experience the greatest shifts in alcohol expectancies and their salience and for whom these shifts are most strongly associated with alcohol consumption. The research findings will bridge the gap between theory, research, and intervention development by evaluating alcohol expectancies and their salience as potential intervention targets while drinking or when in high risk contexts. The proposed application is aligned with NIAAA’s strategic plan and has significant implications for public health, including identifying when to intervene, what mechanisms to target (e.g., alcohol expectancies and/or their salience), and who to target.