The concept of nostalgia has changed substantially both denotatively and connotatively over the span of its 300-year history. This article traces the evolution of the concept from its origins as a medical disease to its contemporary understanding as a psychological construct. The difficulty of tracing a construct through history is highlighted. Attention is paid to roles played first by the medical context, and then by the psychiatric, psychoanalytic, and psychological approaches. Emphasis is given to shifts in the designation of nostalgic valence from bitter to sweet to bittersweet, and the processes of semantic drift and depathologization are explored. Because the sense of nostalgia was constructed and reconstructed within social, cultural, and historical contexts, its meaning changed along with the words used to describe and connect it to other entities. Nostalgia's past illustrates the influence of language, social-cultural context, and discipline perspectives on how a construct is defined, researched, and applied. (PsycINFO Database Record (c) 2013 APA, all rights reserved).