In the economic literature today, discussions flare up from time to time about “grand theories”, which are thought to be lacking in modern economic science and which could counter the trend toward segmentation that breaks it up into loosely interconnected parts. The notion of abstract “grand theories” emerged in sociology and was particularly refined by Robert Merton, who contrasted them with empirically based and testable “middlerange theories,” which sis considered preferable. A classical grand theory in the history of economic science was that of Karl Marx. The theory of general equilibrium of Leon Walras also qualifies to some degree. Subsequently a significant specialization and segmentation of economic theory took place. The economic mainstream has undergone great changes in the past several decades, but the changes have been largely in the direction of greater heterogeneity. Despite some negative consequences of this trend and its critical reception in part of the economic literature, a return to grand theories in the foreseeable future is highly unlikely.