Imagine the following scenario. Susan and Tom have just started dating and are dining at a local restaurant. The service has been slow, and as they wait for the check Tom is furious and wants to complain to the manager. Susan, on the other hand, notes how busy the restaurant has been, and feels sympathy for the overworked, harried waiter – if anything, she wants to leave a large tip. Susan and Tom argue about the matter and leave in a huff.

This sort of interpersonal problem, all too familiar to many of us, arises in part when people have different emotional reactions to events. When individuals' emotions diverge in social interactions, they are left to grapple with their different perceptions, action tendencies, and often uncharitable explanations for why they differ. Had Susan and Tom both felt sympathy for the waiter, they would have agreed on the reasons for the slow service, a course of action, and perhaps felt solidarity in their shared response.

Based on the idea that it is adaptive for relationship partners to have similar emotional reactions to events, we propose that people in close relationships develop increasing similarity in their emotional responses over time – a process we call emotional convergence. Furthermore, we propose that people with less power make more of the change necessary for emotional convergence to occur. In this chapter, we elaborate on the theoretical basis for these hypotheses and draw on recent longitudinal studies of relationships to provide supportive evidence.