In the past 25 years, the demographic shift in higher education toward adult learners has necessitated a comprehensive understanding of their participation patterns. This study aims to synthesize publication trends, methodological characteristics, empirical factors, and the evolution of theoretical frameworks that influence their participation. Following PRISMA 2020 guidelines, a systematic review was conducted on 74 peer-reviewed articles indexed in the Web of Science and Scopus between 2000 and October 2025. Data were analyzed across three time periods (2000–2009, 2010–2019, and 2020–2025) using a hybrid deductive–inductive analytical approach. The results indicated a marked surge in research output after 2020, with a peak of 10 studies in 2023. While quantitative designs and offline modalities were initially predominant, a clear trend existed toward qualitative approaches and technology-mediated learning in recent years. Intrinsic motivation was the most consistent determinant (77.0%), while work–study conflict persisted as a major barrier (21.6%). Notably, institutional determinants and structural frameworks gained prominence after 2020, reflecting a shift from individual-centered to institutionally responsive models in higher education. These findings indicate that adult learners’ participation is shaped by the dynamic interaction of personal motivations, situational constraints, and increasingly salient institutional conditions, reflecting broader transformations in higher education delivery since 2020. Accordingly, advancing adult participation requires multi-level approaches that integrate learner agency with supportive institutional designs and policy frameworks, rather than relying solely on individual motivation.
Park et al. (2026) studied this question.