Between the ages of eighteen months and six years, children acquire about eight words each day without specific instruction or correction, simply through the course of natural conversational interactions. This book brings together investigations from a variety of disciplinary backgrounds (with an emphasis on linguistics, psycholinguistics, and computer science) to examine how young children acquire the vocabulary of their native tongue with such rapidity, and with virtually no errors along the way. The chapters discuss a number of issues relating to the child's mental representation of objects and events on the one hand, and of the linguistic input on the other; and the learning procedures that can accept such data to build, store, and manipulate the vocabulary of 100,000 words or so that constitute the adult state. Taken together, these essays provide a state-of-the art analysis of one of the most remarkable cognitive achievements of the human infant.