The article focuses on the fact that an ecotone as a constructive-geographical concept, is gaining popularity among geographers not only in Ukraine but also in the world. Therefore, the purpose of this article is to substantiate the importance of ecotone as the main form of land surface landscaping. It is established that continuous changes of the landscape environment, caused in our time by both natural and anthropogenic factors, will inevitably cause movement of physical and geographical boundaries. In addition, most landscaping systems are not homogeneous in typology, and the transitions between them are rather blurred. This further complicates the drawing of boundaries and suggests the leading importance in the landscape organization of the terrestrial surface of broad boundary strips – ecotones. The proposed definition of an ecotone emphasizes its role as a major form of terrestrial landscaping. Six types of ecotones have been proposed within the southwestern part of the East European Plain: 1 – mixed forests – deciduous forests; 2 – deciduous forests – forest-steppe; 3 – mixed forests – forest-steppe; 4 – forest-steppe – steppe; 5 – steppe – dry steppe; 6 – dry steppe – semi-desert. As the phenomenon of transitivity is spatially and temporally continuous, most of the land (especially in the temperate zone) is occupied by ecotones or “ecotonic” landscapes. The “border” landscapes are localized in regions with extreme natural conditions. The relationship of “ecotonic” and “boundary” landscapes on the Earth’s surface is illustrated by the terra – ecotone tetrahedron. Formation of ecotones in anthropogenic landscapes (transformed to varying degrees by man) has been taking place since the origin of the reproductive economy, and our studies of the interpenetration of natural and human beginnings in the formation, in particular, of agricultural landscapes indicate that, in terms of geography, this is an enormous field of research. Therefore, the study of ecotones can be the content of a particular branch of landscape science – ecotonistics, which should focus specifically on the study of natural boundaries in different types of landscapes.