Many years of research by authors and generalizations of literary materials are the basis of modern ideas about the sexual structure of mammalian populations. The features of the sex ratio in mammal populations of different taxonomic affiliation, the principles of the dynamics of sexual composition and the mechanisms of regulation of this process, the role of changes in the sexual structure of populations in fluctuations in the number of animals and the influence of anthropogenic factors on intra-population transformations are analyzed. For a wide range of biologists, agricultural workers and university biology students.