Originally published in 1977, this book considers the role language plays in psychological development. It tries to avoid general discussions of "language and thought", an approach already sufficiently developed by philosophers and (although somewhat less) by psychologists. Instead it attempts to focus specifically upon what we can learn about the topic from available research findings at the time. Theoretical considerations are developed only when necessary to clarify an issue or to facilitate the integration of presented material. The aim of the work is simple – to share with the reader the author’s thoughts and understanding of available knowledge of the role of language in mental development.