The developmental origins and determinants of social contingency detection are discussed. Based on recent research, the author proposes that the origins of social contingency detection correspond to the early propensity developing in the first 6 months of life to differentiate between what pertains to the self (i.e., one's own body) and what pertains to others. Furthermore, from the second month of life, what infants appear to gain from contingency detection while interacting with others is a sense of shared experience or intersubjectivity. Research suggests that although the development of intersubjectivity is a central feature of infant behavior and development, the meaning of contingency detection, hence the source of intersubjectivity, changes radically between birth and 18 months of age. In general, it is proposed that the origins and determinants of social contingency detection must be construed in relation to (1) the developing sense of self in infancy, (2) the infant's developing sense of reciprocity with others, and (3) the infant's developing sense of participation with others. The author concludes by proposing a relevant map of changing social stances adopted by infants in the course of early development.