The growth of attention to the meso level analysis in economics, which intensified in the 21st century, is associated with a number of factors. In this paper we draw attention to the following. First, the dissatisfaction with the traditional micro-macro dichotomy, which does not take into account the growing complexity of the economy and is, therefore, insufficient to understand ongoing economic processes and phenomena, including the causes of recurrent and increasing global crises. Second, the dissemination in the scientific discourse of the ideas of Synergetics and the evolutionary-synergetic paradigm of analysis of (socio) economic systems. With this approach, the dynamic structures of the meso level, which ensure interconnected development of the economy, are at the centre of consideration. The methodological differences between approaches to the meso level analysis, characteristics of Heterodox Economics, and Neoclassical Economics based on microfoundations, are shown. The essence of the heterodox approach presented in the paper is that the meso level is viewed as the result of self-organisation of (socio) economic systems in certain material conditions. The meso level of the economy is formed by the stable materially conditioned structures of interrelations and the rules for the joint functioning of the constituent parts (socio-economic system) that ensure the reproduction and stable dynamics of the development of the entire system. Through the prism of the declared methodology, a retrospective analysis of known concepts, primarily the model of Wasiliy Leontief, was carried out. It is shown that the principles of meso level analysis in economics were used long before the term "Mesoeconomics" was introduced into the scientific literature. A methodological analysis of modern Russian concepts is presented – the theory of the "shifting mode of economic reproduction" (V. I. Maevsky) and the "Institutional matrices theory, or X-Y theory" (S. G. Kirdina-Chandler), which investigate the mesolevel of (socio) economic systems. Particular attention is paid to obtaining new results which could not be obtained within the framework of only micro or macro level analysis.