The book extends the concept of language in Lev Vygotsky's Sociocultural Theory to the cognitive differences between second language acquisiton(SLA) and foreign language learning(FLL), and succeeds in filling the gap between FLL and SLA in constructing instructional interaction for FLL by the adoption of the Zone of Proximal Development and Scaffolding. It is not just intended to promote a particular approach to instructional interaction development in online FLL, but is an attempt to highlight the existence of the differences between FLL and SLA, and to underline the necessity to attend to them on a more than SLA theoretical basis.