From the view of Zuengler and Miller (2006, p.37), sociocultural theory is a broad term including Vygotskian sociocultural theory, language socialization, situated learning theory, critical theories of discourse and social relations. In this article, sociocultural theory is equivalent to Vygotskian sociocultural theory, because compared with other sociocultural principles, it has made the greatest contribution to SLA (Ortega, 2009). Vygotskian sociocultural theory is comprised of a series of key concepts: the Zone of Proximal Development (ZPD), scaffolding, mediation, regulation, private and inner speech, activity theory, to name only a few, which play significant roles in SLL/SLA. This article will mainly examine ZPD and scaffolding, and their implications.