DescriptionThis dissertation explores the development of words and categories with the intention of better understanding the organization of the lexicon. Study I investigates lexical organization, lexical access, and categorization in adults. In particular, I contrast the way adults access lexical items with the way they explicitly categorize these items. By testing speakers of two different languages—English and Mandarin—I also explore which aspects of lexical organization are universal and which are linguistically relative. Study II investigates the nature of lexical representation, access, and categorization in two- through nine-year-old typically-developing children. Additionally, I investigate the way developments in categorization do and do not coincide with development of the ability to articulate these categories, with the acquisition of relevant declarative knowledge, and with developments in other cognitive abilities. The results of the first two studies suggest that lexical organization and access are qualitatively different in young children than in adults. Study III investigates the nature of the lexicon and categories in children with autism. I find that although autistic children have many cognitive deficits, they seem to follow typical patterns of category development. Together, these studies improve our understanding of the nature and development of lexical organization, lexical access, and categorization.