The purpose of this review is to characterize major advancements in the past 40 years of research on youth sport motivation. The author focuses on this period, during which the Institute for the Study of Youth Sports, affiliated researchers, and other scholars contributed to the current state of the field. First, she traces paradigm shifts that represent changes in the philosophy and practice of science in youth sport motivation research. Second, she discusses emergent theoretical perspectives that guided empirical research and produced robust findings on predictors, mediators, and outcomes of motivation. Third, she translates these theories and associated studies to inform evidence-based best practices for youth sport programs. Finally, the author recommends that future research highlight developmental approaches, examine sport as a means of promoting physical activity, and consider multidisciplinary perspectives on conducive topics. By reflecting on paradigm shifts and research trends over time, scholars can meaningfully contribute to an increased understanding of youth sport motivation in the decades to come.