Lev Semyonovich Vygotsky (real name Lev Simkhovich Vygodsky; Orsha 1896–Moscow 1934) was a Russian psychologist who created cultural-historical theory, which proved influential in developmental psychology and other psychological disciplines. Vygotsky characterized his approach as “height psychology” (as opposed to “depth psychology”) and posited that the higher forms of mind should be the starting point for the study of human development. In his view it was essential to study psychological processes in their historical dynamics; these dynamics could be unraveled with the causal-genetic approach he developed, which involved the guided formation of mind in the course of its study or the experimental unfolding of ontogeny. Vygotsky claimed that the mechanisms of human development are not genetically determined and that we must find its source in culture and the social environment. Human development is mediated by cultural artifacts and sign systems, which are mastered in a dialogue with other people in spontaneous or guided interaction, which stimulates development by creating a zone of proximal development. The major means of the transformation of innate mind into higher mind is language, which enables us to preserve and transmit the experience of generations. In this process of cultural development the person develops a system of higher psychological functions that are social in origin, voluntary and mediated in nature, and form part of a systemic whole. The process of ontogeny goes through a series of stable periods and crises that correspond with specific conditions of the social situation of development and the developmental tasks. Age periods are completed with the development of neoformations, which do not just form results but are also prerequisites for further development. With the development of verbal thinking and the mastery of cultural means of behavior the person masters her/his innate mind and becomes a personality, whose main characteristic is freedom of behavior.