Relevance. The key factor in the development of any region is its geographical position in the socioeconomic and geopolitical space of the country. In this respect, middle regions are of particular interest. Unfortunately, their unique qualities remain largely underexplored in research literature, which is the gap this article seeks to address. Research objective. The purpose of the study is to provide a definition of the concept 'middle region' , describe its key characteristics and align them with the strategic priorities in the development of such regions. Data and methods. The research methodology centres around the notion of cumulative effect of the middle region and the tools for its assessment. This effect is associated with enhanced socioeconomic efficiency of a territorial capital resulting from the advantages of its middle position. Among other things, this effect manifests itself through higher economic returns on investment. The empirical part of the study relies on the data on 36 Russian middle regions, their missions and priorities of strategic development. Results. The article summarizes the Russian and international theoretical approaches to the definition of the middle regions, their place and role in the territorial structure of a country and its socioeconomic development. It is shown that most authors assign middle regions the role of the country's epicenter, highlighting their key role in economy, culture, politics and other spheres of life. The approach proposed in this study focuses on middle regions' position in space, on the one hand, and, on the other, sees them as systems of interactions in the socioeconomic space. Based on this understanding of the middle region, several groups of Russian middle regions are identified: integrators, sustainable middle regions and developing middle regions. Conclusions. The mission of middle regions is one of the fundamental concepts of strategic management, comprising a hierarchy of goals. It is shown that although the mission of middle regions should be to become integrators of the country's socioeconomic space through the network of inter-territorial and global interactions, not all Russian middle regions are ready to pursue this ambitious goal and prefer to focus on addressing internal goals of their own.