Lev Semyonovich Vygotsky (Russian: Лев Семёнович Выготский, [vɨˈɡotskʲɪj]; Belarusian: Леў Сямёнавіч Выгоцкі; November 17 [O.S. November 5] 1896 – June 11, 1934) was a Soviet psychologist, best known for his work on psychological development in children and creating the framework known as cultural-historical activity theory. His major ideas include: The Social Origin of Mind: Vygotsky believed that human mental and cognitive abilities are not biologically determined, but instead created and shaped by use of language and tools in the process of interacting and constructing the cultural and social environment. The Importance of Mediation: He saw mediation as the key to human development, because it leads to the use of cultural tools and becomes a pathway for psychological development through the process of interiorization. The Zone of Proximal Development: Vygotsky introduced the concept of the ZPD which refers to the gap between a child's current level of development and the level they are capable of reaching with tools provided by others with more knowledge. The Significance of Play: Vygotsky viewed play as a crucial aspect of children's development, as the best sandbox to build and develop practice of mediation. Source: Wikipedia (en)