In this paper, the role and nature of language and language development will be discussed. Research and theory in second language acquisition has demonstrated that (i) language is an abstract, implicit and complex system. Input (ii) plays a key role in language development; despite the fact that some knowledge of language is innate (iii). Overall, language development (iv) is ordered and stage-like and instruction (v) has a limited role. Theoretical and pedagogical implications will be highlighted.