Exploring language development from birth, this accessible textbook introduces the field of child language acquisition, establishing key theoretical debates. It considers what characteristics of the human mind make it possible to acquire language and to what extent acquisition is biologically programmed and influenced by our environment. It inquires as to what makes second language learning (in adulthood) different from first language acquisition; and whether the specific stages in language development are universal across languages. It will be a key text for courses in linguistics, developmental psychology and cognitive science.