Lev Vygotsky's cultural-historical psychology is a "grand theory" that attempts to provide a unifying approach for the discipline of psychology. This chapter introduces Vygotsky's cultural-historical psychology without oversimplifying the theoretical ideas but at the same time making his sometimes complex ideas accessible. Vygotsky traces the development of various forms of speech from external social speech through to internal private speech to show how humans develop the ability to master themselves, to control and regulate their own mental functions. The significance of Vygotsky's psychological tools is that they provide a bridge between the development of human culture and the cultural development of the human child. According to Vygotsky, the potential concept is a "pre-intellectual formation arising very early in the development of thinking". Vygotsky identified different structures or kinds of generalization that arise during the course of development of concepts.