How are word meanings represented in the human mind and woven together when we string words into sentences? How do children learn what words mean and how to use them? Representations of word meaning have become increasingly important in linguistic theories and new methodologies are now being widely used to study them. In computational linguistics, new algorithmic and statistical techniques are being applied to on-line texts to provide the basis for lexical analyses, and machine-readable dictionaries have provided a starting point for building lexicons for natural language processing systems. These technologies make large amounts of data and powerful data-analysis techniques available to theoretical linguists, who can repay the favour to computational linguists by describing how one efficient lexical system, the human mind, represents word meanings. Lexical semantics provides crucial evidence to psychologists, too, about the innate stuff out of which concepts are made. Finally, it has become central to the study of language acquisition. Infants do not know the grammar of the language community they are born into but they do have some understanding of the conceptual world that their parents describe in their speech. Since concepts are intimately tied to word meanings, children's knowledge of semantics might play an important role in allowing them to break into the rest of the language system. This book offers views from a variety of disciplines of these sophisticated new approaches to understanding the mental dictionary.