This chapter reviews theory and research on interpersonal attraction, a literature that dates back more than half a century. Although this literature has produced a wealth of empirical data, it also has lacked theoretical coherence. The present chapter takes two significant steps toward the theoretical unification of this literature. First, it identifies three metatheoretical perspectives-the domain-general reward perspective, the domain-specific evolutionary perspective, and the attachment

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... pective-that collectively account for the large majority of research findings on interpersonal attraction, and it reviews the literature from within that metatheoretical structure. At their core, all three of these perspectives emphasize the needs people bring to attraction contexts. Second, it suggests that the instrumentality principle-that people become attracted to others to the degree that those others help them achieve goals that are currently high in motivational priority-is the core, unifying principle underlying interpersonal attraction. According to this principle, people also become less attracted to others who are instrumental for a certain goal once people have made substantial progress toward achieving that goal, because people tend to shift their emphasis to other goals at that point. Indeed, because people's motivational priorities can fluctuate rapidly, their attraction to a given target person, and their rank ordering of attraction to others in their social network, will also fluctuate.