In the article, the researcher attempts to discuss the essence the Vygotsky's cociocultural theory and its contributions to the better understanding and instruction take place in the foreign language classroom. The researcher presents the basic assumptions of sociocultural theory, and discusses how these assumptions differ from the mainstream second/foreign language acquistion theory and research, especially Nativist theories of SLA. From the sociocultural stance,acquiring a second language entails more thatsimple mastery of the linguistic properties of the L2. It encompasses the dialectic interation of two ways of creating meaning in the world (interpersonally and intra-personally). Several important concepts of Vygotsky's sociocultural theory-Semiotic mediation in the ZPD (Zone of the Proximal Development), Private Speech, and the Activity Theory-are discussed thoroughly in the context of foreign language education. Semiotic mediation in the ZPD characterizes how learning occurs in social interaction. Learner's private speech,defined as the convergence of thought and language by Vygotsky,is the tool to regulate thinking, and then, helps speakers seek solutions and move to self-regulation. By the activity theory, Vygotsky maintains that learning is a situated activity, which occurs in social interaction and social context. Learners bring in their goals, actions, background and beliefs,interacting with the task they are engaged in. The article concludes with much implication the cociocultural theory has brought to the foreign language learning, instruction, and research. It has contributed powerful theo-retical frameworks that can be used to better understand and analyze the dynamics of class-room instruction.