After more than a decade of research the Bristol Study of Language Development has assembled a corpus of data on the language development of children aged one to five years that is representative both in terms of the sample of children studied and of the situations in which their spontaneous speech was recorded. In this book Gordon Wells, who directed the project, presents a detailed account of the common sequence of development that was observed, specifying the ages at which linguistic categories emerged and the frequencies with which they were used at successive ages. The data have been rigorously analysed and the book also advances possible explanations for the developmental sequence identified. Variations within the overall pattern did of course occur and some of the more salient aspects are also discussed. The latter part of the book discusses the influence of environmental factors and in particular the role of adults in facilitating language development.