Lev Vygotsky, Belarusian-Russian psychologist and philosopher (d. 1934)
Lev Semyonovich Vygotsky (Russian: Лев Семёнович Выго́тский; Belarusian: Леў Сямёнавіч Выго́цкі; November 17 [O.S. November 5] 1896 – June 11, 1934) was a Soviet psychologist, known for his work on psychological development in children. He published on a diverse range of subjects, and from multiple views as his perspective changed over the years. Among his students was Alexander Luria and Kharkiv school of psychology.

He is known for his concept of the zone of proximal development (ZPD): the distance between what a student (apprentice, new employee, etc.) can do on their own, and what they can accomplish with the support of someone more knowledgeable about the activity. Vygotsky saw the ZPD as a measure of skills that are in the process of maturing, as supplement to measures of development that only look at a learner's independent ability.

Also influential are his works on the relationship between language and thought, the development of language, and a general theory of development through actions and relationships in a socio-cultural environment.

Vygotsky is the subject of great scholarly dispute. There is a group of scholars who see parts of Vygotsky's current legacy as distortions and who are going back to Vygotsky's manuscripts in an attempt to make Vygotsky's legacy more true to his actual ideas.