Today's fragmentation of the world economy, the emergence in the near future of large economic blocs operating in different ideological and conceptual models of economy and society, and the fierce struggle for resources and influence, logically lead us turn to history, including the recent one. The issue of the functioning and collapse of the socialist monetary community has another, more specific but also topical meaning. It has to do with understanding the mechanisms of disintegration of the European Union and the euro area, its management and eventual overcoming. In this paper, we focus on the study of monetary mechanisms within the socialist system, and more specifically on its model of integration, the Comecon, which lasted from 1949 to 1991. In the first part we present the basic principles of socialist integration and the role of international socialist money. In the second part we present the main stages in the evolution of the monetary mechanisms of Comecon. The third part is devoted to some technical problems of multilateral payments and the peculiarities of the transfer ruble. Finally, we try to compare with European Payment Union. We present some competing hypotheses, answering the question why the monetary system of Comecon failed.