This dissertation is an ethnographic study of the co-transformation of youth and religious institutions. It looks at how religion socializes youth to embody particular gendered ideals about morality and how youth, encountering these ideals, reinterpret them. It focuses on boys and young men who temporarily ordain as Buddhist monastics for several years in northern Thailand. Locating the construction of monastic masculinity—what it means to be a morally good man and ideal monastic—within interpersonal moments among monastics and between lay and monastic communities, this dissertation makes three broad arguments. First, the internalization of religious ideals is not a linear development across the life course. While adult monastics may adjust their bodily behavior to effect changes to their inner state of mind, boys’ bodily adjustment to temporary monasticism is about performing social cohesion. The longer youth remain monastics, the more difficult this performance becomes as maintaining strict adherence to their ascetic rules becomes onerous. At the same time, lay supporters, whose generosity monastics depend upon, have high expectations that monastics will strictly follow their ascetic rules. Monastic and lay communities develop “asymmetrical orientations” towards the rules to find a middle ground between expectations and obligations. Second, notions that only certain kinds of men are morally capable of ordaining demonstrates the co-construction of gender and morality in the reproduction of dominant masculinities. Finally, this dissertation demonstrates how religious institutions like Buddhist monasticism may be not only a force for social reproduction and nation building but for effecting social change.