This chapter focuses on the historical contingency and cross-cultural plurality in codes of “emotional development,” a value-laden and culturally embedded concept. What counts as healthy or virtuous emotional experience, comportment, or growth among children and youth (and in other stages in the life cycle) varies significantly over time and place. The plurality of emotional codes also means that an individual might experience either unfamiliarity with the codes of emotional behavior in a given context, or sometimes become aware of conflicting sets of emotion rules. While “formation” designates the culturally specific codes of affective comportment and expression, and the process through which the individual child incorporates and embodies these codes, this chapter introduces the concept of “emotional frontiers” to describe the affective experience of encountering a boundary between different affective formations or divergences within the same formation. A frontier may be encountered in various ways—from a little misunderstanding to a violent confrontation.