Now in its fourth edition, this textbook provides a chronological account of first language acquisition, showing how young children acquire language in their conversational interactions with adult speakers. It draws on diary records and experimental studies from leaders in the field to document different stages and different aspects of what children master. Successive chapters detail infants' and young children's progression from attending to adult faces, gaze, and hand motions, to their first attempts at communicating with gaze and gesture, then adding words and constructions. It comprehensively covers the acquisition of the core areas of language - phonetics and phonology, lexicon, grammar and sentence structure, and meaning - as well as how children acquire discourse and conversational skills. This edition includes new sections on how children build 'common ground' with adults and other children, individual differences in children's language development, how they collaborate with adults in constructing utterances, and how they qualify beliefs.