Social scientists, biologists, and behavioral psychologists have extensively explored the sources of reciprocal behavior and the conditions for the sustainability of reciprocity in various categories of interactions. Consider these oft-quoted colloquialisms: “Do unto others as you would have done unto you.” “If you scratch my back, Ill scratch yours.” “Tit for tat.” These pieces of collective wisdom come to mind for many people when they think of reciprocity. In the existing social science literature, the term reciprocity refers to a broad range of concepts. In an attempt to distinguish different economic concepts of reciprocity, this entry provides a taxonomy of reciprocity, which includes the concepts of structural reciprocity, stochastic reciprocity, and induced reciprocity.

The idea of reciprocity assumes peculiar importance in a world where there is ...