Economists are looking for microfoundations of macroeconomics. Since an individual’s choices are constrained by decisions that cannot be interpreted as resulting from aggregation of individual preferences, we can also set the problem of what are the macrofoundations of microeconomics. There is a level of analysis that may help to solve both problems. It is the analysis of the interrelations between industry and markets as it has been carried out by Pasinetti (1981) in his Structural Change and Economic Growth. Some additional help to the understanding of these problems can come from a critical assessment of the rationality assumption that is usually made about individuals’ behaviour in microeconomics. In this chapter I shall try to move in this direction, by showing why rationality criteria for the system cannot be reduced to individual rational criteria as they have been defined in the context of utilitarism. Our analysis suggests that the two problems are interlinked.