D. B. Elkonin's theory of child's development is systematically presented; particular attention is given to his general scientific principles, methodology, and basic theoretical views. The phenomenon of childhood appears, as the result of the authors' analysis, as both social-cultural and psychological subject-matter. The first step in the study of the phenomenon consists in the recognition of the necessity to distinguish between the developmental and the historical crises of its existence. Contemporary outlook of the phenomenon, is described as abounding with crises.