Book excerpt: There are between 4,000 and 6,000 languages remaining in the world and the characteristics of these languages vary widely. How could an infant born today master any language in the world, regardless of the language’s characteristics? Shelia M. Kennison answers this question through a comprehensive introduction to language development, taking a unique perspective that spans the period before birth through old age. Introduction to Language Development offers in-depth discussions on key topics, including: the biological basis of language, perceptual development, grammatical development, development of lexical knowledge, social aspects of language, bilingualism, the effect of language on thought, cognitive processing in language production and comprehension, language-related delays and disorders, and language late in life.