Abstract
Nostalgia is a self-conscious, bittersweet but predominantly positive and fundamentally social emotion. It arises from fond memories mixed with yearning about one's childhood, close relationships, or atypically positive events, and it entails a redemption trajectory. It is triggered by a variety of external stimuli or internal states, is prevalent, is universal, and is experienced across ages. Nostalgia serves a self-oriented function (by raising self-positivity and facilitating perceptions of a positive future), an existential function (by increasing perceptions of life as meaningful), and a sociality function (by increasing social connectedness, reinforcing socially oriented action tendencies, and promoting prosocial behavior). These functions are independent of the positive affect that nostalgia may incite. Also, nostalgia-elicited sociality often mediates the self-positivity and existential functions. In addition, nostalgia maintains psychological and physiological homeostasis along the following regulatory cycle: (i) Noxious stimuli, as general as avoidance motivation and as specific as self-threat (negative performance feedback), existential threat (meaninglessness, mortality awareness), social threat (loneliness, social exclusion), well-being threat (stress, boredom), or, perhaps surprisingly, physical coldness intensify felt nostalgia; (ii) in turn, nostalgia (measured or manipulated) alleviates the impact of threat by curtailing the influence of avoidance motivation on approach motivation, buttressing the self from threat, limiting defensive responding to meaninglessness, assuaging existential anxiety, repairing interpersonal isolation, diminishing the blow of stress, relieving boredom through meaning reestablishment, or producing the sensation of physical warmth. Nostalgia has a checkered history, but is now rehabilitated as an adaptive psychological resource.