How Languages are Learned (3rd ed.) by Patsy M. Lightbown and Nina Spada. Reviewed by Youngsoon So In the introduction to a collection of articles on second language acquisition naturalistic, instructed, or both – has long been a common activity for a majority of the human species and is becoming ever more vital as second languages them- Considering the diversity of SLA contexts and different factors/variables involved in these contexts, a single teaching method is unlikely to guarantee the best results. Therefore, language teachers need to be according to the demands of their immediate teaching context. In this respect, Patsy Lightbown and Nina Spada’s How Languages are Learned is a good resource for all language teachers, those in SLA in particular, in that it provides a comprehensive overview of what factors have been proven, disproven, or still left unproven to SLA processes and outcomes and how variable the effects of different factors can be in each language learning/teaching context. Although not segmented in this way by the authors, the book can be divided The introduction serves as a general guideline to provide readers with an overview of the topics to be discussed in later chapters. The authors also provide an informal survey asking the readers’ beliefs about a range of SLA processes and outcomes, issues the authors ask readers to keep considering while reading the rest of the book. In the closing chapter positions by elaborating each survey point. This circular format is a good way to help readers actively relate their own thoughts and experience to the reading and see whether there is any difference between their thoughts and the opinions sup- ported by literature. develop- ment acquisition has been thought to be the foundation on which SLA processes can be explained, if acquisition are taken into account. As such, the authors begin with a chapter outlining and evaluating three behaviorist, innatist, and interactional/ developmental perspectives. authors argue for childhood bilingualism. The second part consists of four chapters (Chapters 2-5) dealing with different aspects of SLA: SLA theories (Chapter 2), individual learner differences in SLA