This volume, focusing on Japanese as a second language (JSL), is part of the Language acquisition and language disorders series by Benjamins. As the editor points out in the introductory chapter, there is a pressing need to investigate the acquisition of languages other than English and other European languages if SLA claims to be a discipline broad enough to encompass acquisition of any second language (L2). In particular, given the importance of Japanese as one of the most commonly studied languages in Asia and the fact that Japanese has many linguistic features not found in European languages, research on the acquisition of JSL should have important implications for both practical applications in language teaching and theoretical investigation of language universals, innate principles, and the like.