This chapter examines some major theories of language development. It considers the impact of infant-directed speech (IDS) and child-directed speech (CDS) on the child’s language development. The chapter explains language in its cultural context, including the role of adults and peers in guiding children’s communication skills. It highlights narrative and story-telling in developing children’s mind-mindedness, and the importance of this in facilitating the transition from oracy to literacy. The chapter explores some literacy programmes in schools as well as methods, including collective argumentation, that facilitate the development of thinking and critical skills through collaborative discussion. Language competence is crucial for emotional well-being, social functioning and thinking capacity across the lifespan and in all cultures. Experience of internal-state language continues to be related to children’s subsequent understanding of their own and others’ internal states. More research demonstrates that bilingual children outperform monolingual children on verbal and non-verbal measures of intelligence.