The remarkable way in which young children acquire language has long fascinated linguists and developmental psychologists alike. Language is a skill that we have essentially mastered by the age of three, and with incredible ease and speed, despite the complexity of the task. This accessible textbook introduces the field of child language acquisition, exploring language development from birth. Setting out the key theoretical debates, it considers questions such as what characteristics of the human mind make it possible to acquire language; how far acquisition is biologically programmed and how far it is influenced by our environment; what makes second language learning (in adulthood) different from first language acquisition; and whether the specific stages in language development are universal across languages. Clear and comprehensive, it is set to become a key text for all courses in child language acquisition, within linguistics, developmental psychology and cognitive science.