英國語言學教授韓禮德 (M. A. K. Halliday)曾說，他喜歡從各種可能的角度與路徑研究語言，而其中又以社會取向的觀點看待語言是他認為最能捕捉語言本質的觀點。本期特刊承襲韓禮德的看法，試圖以多元的取向探討華語文做為第二語言的習得與教學。收錄的四篇文章分別從認知運算、語言發展、複雜系統、及生態語言學的角度切入，介紹相關的理論與實徵研究。這些不同的取向都將第一語和第二語的習得視為同一種現象，可以用相同的一套理論解釋，並用以引導教學。這套理論將語言看成同時是一種認知的工具、也是社會的工具，是人類文明創造出來的產物，也同時創造了人類的文明。這種觀點符合當代興起的生態認知觀點，希望能對二語習得及華語文教學有所啟發。

Michael Halliday advocated the idea of studying language from every possible vantage point, but favored the social angle himself. The Special Issue adopts Halliday’s perspective and includes four articles that look into first and second language acquisition and teaching from the cognitive/computational, language development, complex dynamic system, and ecological linguistics standpoints. Both theoretical and empirical works in the literature are summarized in the hope of offering a new take on second language acquisition in general and on teaching and learning Chinese as a second language in particular. The various approaches share the same assumption that learning a first language and a second one are driven by the same cognitive and social mechanisms which are ecologically tuned. This is because language is fundamentally both a cognitive and a social tool.