PROJECT SUMMARY Young adulthood (ages 18-25) is a critical developmental period during which individuals often escalate or mature out of substance use. Indeed, young adults (YA) use cannabis at the highest rate of any age group, with 35% reporting past year use, thus it is critical to identify factors associated with hazardous cannabis use given the potential impact on this vulnerable developmental group. Heavy cannabis use among YA is related to poorer health later in life, deleterious long-term effects on cognition, engagement in hazardous behaviors while under the influence (e.g., driving), and myriad other cannabis-related problems. As such, it is imperative to understand factors that influence the time course of cannabis use patterns and mechanisms underlying transition from casual to heavy or hazardous use levels. Notably, young adulthood is characterized by frequent, smaller-scale transitions (i.e., micro-transitions) and critical life events that can lead to an escalation or reduction in cannabis use, likely depending on their subjective evaluation (i.e., valence). Certain transitions may increase cannabis use frequency (e.g., college entrance), while others may be protective (e.g., marriage). A behavioral economic (BE) framework can help explain how micro-transitions during young adulthood influence prospective changes in cannabis use. BE domains are influenced by internal (e.g., craving) and external (e.g., new employment) influences and include (1) access to and preference for alternative reinforcers (i.e., lack of alternative activities that compete with cannabis), (2) discounting of delayed rewards (i.e., inordinate preference for smaller immediate rewards, such as positive cannabis effects), and (3) relative cannabis value (i.e., demand; willingness to pay prohibitively high prices for cannabis despite limited resources or income). Further, motives for cannabis use (e.g., coping, enhancement) are key variables that likely account for the relation betwe