The importance of reciprocity is not new in economics. Contractual market exchanges and long-run interactions are both situations based on selfinterested reciprocal behaviour. However, reciprocity is not only a behaviour but also a motive that sometimes appears to be inconsistent with self-interest. This fact produces a tension between those who try to explain reciprocal behaviour within the standard framework and those who aim at enlarging it with the introduction of additional behavioural principles. This special issue collects a selection of papers presented at the International Conference ‘‘Reciprocity. Theory and facts’’ were the two perspectives were compared and discussed. In this Introduction note we provide first a broad view of the role of reciprocity in economics and then a quick introduction to each of the contributions enclosed in this special issue.