In the past, most of the soils were considered monogenetic bodies; their genesis was explained on the basis of the analysis of existing environmental conditions and soil processes. In the recent decades, it has been proved that soil polygenesis is a rule rather than an exception. The phenomenon of soil polygenesis can be diagnosed and studied in the field. For example, the presence of the second humus horizon in the soil profile, relict humic material in pockets and cryogenic fissures, and complex layered cutans on the walls of fissures are the indices of soil polygenesis. In this context, micromorphological studies can contribute to the study of soil polygenesis. An impetus to these studies was given by the recognition of the phenomenon of lithological heterogeneity or discontinuity in many soils that were earlier considered to be developed from homogenous substrates. The lithological heterogeneity can be diagnosed with the help of soil micromorphology. Moreover, the following indices should be studied in detail: (1) the size distribution of mineral grains in the soil profile; (2) the mineral composition of the grains of particular size fractions in the soil profile (the sand fraction is considered to be most informative); (3) the features attesting to the mode of deposition of the soil parent materials (eolian, fluvial, glaciofluvial, etc.). As shown by Tursina and Gerasimova, micromorphological features of soils can be important indicators of soil polygenesis. Thus, the microfabric of soil horizons in general and some details (microforms of humus, phytoliths, type of porosity, structural arrangement of the soil mass, iron and salt neoformations, clay separations, etc,) should be studied. Primarily, the changes in the character of microfabric in the soil profile should be analyzed. Thus, If particular horizons in the illuvial part of the profile have similar textures and chemical compositions, but differ in their microfabrics, the initial heterogeneity of the substrate can be recognized/identified/deduced. In Vologda oblast, loesslike well aggregated Bt horizons are underlain by blocky Bt horizons with fissures filled with optically oriented clay. This sequence can be considered to be the result of different depositional cycles (eolian sediments underlain by glaciofluvial sediments). Differences in microfabrics of soil horizons in irrigated soils of Turkmenia were studied by Minashina. On this basis, she distinguished the layers of old/earlier-irrigated soils buried under eolian sediments.