Despite featuring prominently in religions and legal frameworks, and being discussed by anthropologists and sociologists in relation to rights and obligations in society, reciprocity has not received the attention it deserves in the (im)politeness literature. This article proposes and defines the Principle of (Im)politeness Reciprocity, which concerns the (mis)matching of (im)politeness across participants in interaction – something which can be construed in terms of a debit-credit balance sheet. We claim that this principle, driven by morality, is a fundamental mechanism in shaping (im)politeness in interaction and triggering the search for (im)politeness implicatures. We show how it impacts on various kinds of (im)politeness and interacts with context, especially power. The latter part of the article, focusing on requestive exchanges, is more quantitative in orientation, involving studies based on informant testing and corpus analysis. These reveal, for example, that (im)politeness matching is by far the most common interaction, that mismatches are perceived as clear deviations, and that certain kinds of (mis)matching are associated with specific contexts (e.g. school classroom interaction is associated with downward shifts from polite to less polite). Finally, we briefly discuss future research avenues. •The Principle of (Im)politeness Reciprocity is proposed.•Morality is claimed to be fundamental to (im)politeness reciprocity.•How reciprocity shapes interactions and triggers (im)politeness implicatures is revealed.•How reciprocity impacts on and interacts with context, especially power, is revealed.•How reciprocity works in the context of requestive exchanges is revealed.