The genesis of soils with the second humus horizon (SHH)-the most striking relict feature in the profiles of soddy-podzolic (Retisols) and gray (forest) soils (Luvisols)-is discussed. The Middle Holocene radiocarbon age of the SHH, its dark color, and the discrepancy of its properties and the properties of modern humus horizons of forest soils have specified the main issues in the study of SHH: the character of climate changes and shifts of the boundaries of natural zones in the Holocene and the reflection of these changes in the evolution of the soil profiles. We consider the history of studies, systematization, geographic distribution, and modern properties of the SHH. On the basis of the analysis of Holocene paleosols, we try to characterize the prototype of the SHH, to estimate its age, and to trace stages of its development in the Holocene. We have also tried to find analogous soils with the SHH outside of Russia. According to the accepted hypothesis, SHHs are residual paleoclimatogenic formations. Other hypotheses consider them as buried horizons, a result of paleohydromorphism, etc. Dark humic substances of SHHs were formed in the first half of the Holocene and are characterized by extremely high stability. This allows them to survive in the aggressive environment of the eluvial horizons of Retisols and Luvisols. Under the influence of biochemical and mechanical (tree uprooting) factors, SHHs are strongly transformed, which complicates their study. At the same time, well-preserved Chernozems and darkcolored Phaeozems buried under kurgans and other earthy structures and sediments make it possible to establish the prototype of the SHH and to trace its degradation in the late Holocene. Within the East European Plain, the thickness and age of the SHH vary in agreement with the hypothesis of the residual paleoclimatogenic genesis of this horizon. The validity of the hypotheses of the buried nature and hydrogenic origin of the SHH is discussed. At present, interest in soils with the SHH in Russia has somewhat weakened. In Central Europe and North America, soils with the SHH have not been studied, but research into the problem of relict chernozems is being actively pursued. In our opinion, the combination of these two types of objects and, accordingly, the directions of research can lead to more definite conclusions about the origin and evolution of soils with the SHH.