One of the most remarkable developmental feats of human children is the acquisition of language. Speaking and understanding are immensely complicated tasks that no other species has mastered. The question of how children acquire language is one that has occupied the careers of many developmental psychologists. Although that question remains far from completely answered, enormous progress in our understanding of the time course of acquisition and the factors that influence it has been made in the past half- century.

In the first section of this Topic, we sketch the major milestones in language acquisition, from exploratory babbling to the production of grammatically correct sentences. In the second section, we delve into the mechanisms that allow human infants to acquire language and the theories behind the psychology of language acquisition. In the third section, we discuss two interesting cases in which language acquisition does not follow the normal pathway: deafness and Williams syndrome.