One approach to moral economy wishes to show that it is rational to be moral. As rational morality has received little attention from economics, as opposed to political philosophy, this article examines it in an economics framework. Rational morality refers primarily to individual behaviour so that one may also speak of it as moral microeconomics. When a group of agents are disposed to constrain their maximisation, that behaviour may be considered rational. However, this relies on ‘moralised’ assumptions about individual behaviour. Constrained maximisation may also rely on repeated interactions within social structures that then transmit information thus serving as enforcement mechanisms. In this way agents obtain knowledge of others’ past behaviour and choose their interlocutors accordingly. Thus, it pays to behave morally as it will attract similarly disposed agents to participate in cooperative ventures for mutual advantage. An analysis of rational morality on the individual level demonstrates how this moral microeconomy affects social structures, society as a whole, and economic institutions and the moral macroeconomy.