This chapter describes closely related theories of human development that are rooted in the writings of the early twentieth-century Russian psychologist, L. S. Vygotsky. Within this approach, learning and development are seen to occur from the outside in; that is, in contrast to theories that presume the environment to be a mere trigger for genomic expression, or which posit linear stage development that is largely a function of biological maturation, Vygotskian sociocultural theory argues that human mental development is fundamentally constructed through engagement with cultural practices, artifacts, and milieus. In this way, sociocultural/cultural-historical approaches emphasize the dialectical relationship between ontogenesis (an individual’s development across the life span) and the social and material conditions of everyday life, including those comprising formal instructional settings. This chapter begins with a discussion of contemporary theories associatedwith Vygotsky’s ideas
and the core constructs and perspectives that are central to them, namely mediation, internalization, the relationship between biology and culture, and the Zone of Proximal Development. This is followed by a discussion of the contemporary application of sociocultural theories to second language learning and educationally related research and pedagogy.