The assumption of rationality is central in current economic theory. This hypothesis is the pillar for the creation of the homo economicus of conventional theory. Starting with Adam Smith’s approach to rationality, the aim of this paper is to contribute to the discussion of the main characteristics of the individual underlying the rational man of economics and their implications for economic analysis. The meaning of rationality in several authors is reexamined and it is argued that the basis of Adam Smith’s work are still valid.