This chapter discusses the necessary components of second language acquisition, that is, input, interaction, and output. While all language learning theories support the importance of input (written and spoken), they diverge in ways which input is connected to second language acquisition. The chapter then examines some of the second language acquisition theories, such as the interaction hypothesis, the noticing hypothesis, the cognitive-interactionist approach, the output hypothesis, and sociocultural theory, all of which explains how interaction leads to second language acquisition. The chapter moves onto specific pedagogical frameworks that support interaction, including communicative language teaching and task-based language teaching. Finally, the chapter delves into the role that output plays by discussing its functions for second language acquisition.

This chapter focuses on instructed second language acquisition research that examines second language learning specifically in instructional contexts, broadly construed (e.g., classrooms, online learning, self-study). The scope of the research field is discussed by distinguishing it from broader second language acquisition research. In essence, the chapter addresses the primary question that researchers and teachers are interested in: Can instruction help learners develop their second language proficiency? The chapter then answers the follow-up question which is: Which types of instruction are more or less helpful? In answering this question, the chapter considers the goals that learners and other stakeholders, such as teachers and parents, have for their second language development. It discusses different types of second language knowledge (implicit and explicit knowledge) as the goal of second language instruction. Finally, the chapter explores pedagogical issues and ends by considering a taxonomy that describes various approaches and methodologies to second language teaching.

Over the past few decades, various external and internal challenges have increasingly required Vietnam to build up its capacity in the era of globalization by improving the English language competences of both learners and language teachers. Vietnam has responded to these challenges through a number of reforms, most recently the ambitious National Foreign Language Project (NFLP-2020). Overall, the project aims to replace the traditional approach to English language learning and teaching with a more communicative approach and to introduce international standards in English language teacher education (ELTE). Much as these attempts are necessary and effective in certain ways, this chapter argues that they might be too ambitious and counterproductive as they fail to take into account the sociocultural, economic and political contexts of Vietnam. The chapter therefore calls for a critical perspective on these current reforms of ELTE in Vietnam.