Although psychologists have paid scant attention to the sense of obligation as a distinctly human motivation, moral philosophers have identified two of its key features: First, it has a peremptory, demanding force, with a kind of coercive quality, and second, it is often tied to agreement-like social interactions (e.g., promises) in which breaches prompt normative protest, on the one side, and apologies, excuses, justifications, and guilt on the other. Drawing on empirical research in comparative and developmental psychology, I provide here a psychological foundation for these unique features by showing that the human sense of obligation is intimately connected developmentally with the formation of a shared agent “we,” which not only directs collaborative efforts but also self-regulates them. Thus, children's sense of obligation is first evident inside, but not outside, of collaborative activities structured by joint agency with a partner, and it is later evident in attitudes toward in-group, but not out-group, members connected by collective agency. When you and I voluntarily place our fate in one another's hands in interdependent collaboration – scaled up to our lives together in an interdependent cultural group – this transforms the instrumental pressure that individuals feel when pursuing individual goals into the pressure that “we” put on me (who needs to preserve my cooperative identity in this “we”) to live up to our shared expectations: a we > me self-regulation. The human sense of obligation may therefore be seen as a kind of self-conscious motivation.