This article analyzes the role of emotions in social interaction and their effects on social structuration and the emergence of micro-social order. It argues that facial expressions of emotion are key in generating robust patterns of social interaction. First, the article shows that actors' encoding of facial expressions combines hardwired physiological principles on the one hand and socially learned aspects on the other hand, leading to fine-grained and socially differentiated dialects of expression. Second, it is argued that decoding facial expression (...) is contingent upon this combination so that reciprocal attributions of emotional states, situational interpretations, and action tendencies are more effective within rather than across social units. Third, this conjunction affects the conditions for emotional contagion, which is argued to be more effective within social units exhibiting similar encoding and decoding characteristics, and thus aligns emotions and action tendencies in a coherent, yet socially differentiated way. (shrink)