Introduction: Emotion regulation is thought to develop substantially from late adolescence into early adulthood; further, the rate of development purportedly varies based on personal and contextual characteristics. However, little research has explicitly documented this maturation in young adulthood or identiied its determinants. We aimed to (1) characterize how adaptive (positive reappraisal, emotional social support-seeking) and maladaptive (suppression, substance use coping) emotion regulation strategies changed over time and (2) predict change in each strategy based on baseline personal, social, and motivational characteristics. Methods: We followed a sample of 1578 students entering university in the northeastern United States across their irst two years, assessing them four times. Results: As expected, social support-seeking increased and suppression decreased. However, contrary to expectations, cognitive reappraisal declined over time while substance use coping increased. Women generally used more adaptive emotion regulation strategies than did men; social engagement and connection and eudaimonic well-being were generally predictive of using more adaptive coping over time. Conclusions: Overall, students did not consistently demonstrate maturation to more adaptive emotion regulation and in fact exhibited decrements over the irst two years of college. Students' baseline characteristics accounted for substantial degrees of change in emotion regulation. These indings suggest potentially fruitful directions for interventions to assist college students in developing more adaptive emotion regulation skills.The college transition can be especially challenging for young adults, who must navigate stressful academic, interpersonal, and social demands with less reliance on family support and expectations for increasingly self-directed and independent behaviors (Arnett, 2016;Lee & Jang, 2015;Zahniser & Conley, 2018). The experiences in the irst semester or year of college can strongly inluence later academic and achievement outcomes. As a result, colleges and universities provide signiicant support and resources for irst year students; however, those institutional supports decrease signiicantly by the second year despite growing evidence that the transition to second year is associated with increased academic and interpersonal stressors and adjustment dificulties (Conley, Shapiro, Huguenel, & Kirsch, (2020); Ishitani, 2016;Tobolowsky & Cox, 2007). The second year also entails managing important developmental and academic milestones, such as resolving identity issues, developing a sense of purpose, gaining functional independence, solidifying major area of study, and navigating more intense interpersonal relationships (Black, 2014;Sterling, 2018).These irst two years of college may be a critical period for developing effective emotion regulation skills. Emotion regulation refers to the processes of modifying emotions, including which, how, and when they are experienced and expressed (Gross, 2008;Nolen-Hoeksema, 2012). E...