This volume introduces the field of child language development studies,and presents hypotheses in an accessible,largely non-technical language,aiming to demonstrate the relationship between these hypotheses and interpretaions of data,lt makes the assumption that having a theory of language development is as important as having reliable data about what children say and understand,and it advocates a combinaton of both rationalistand moreempiricisttraditions,ln fact,the author overly argues that different traditions provide different pieces of the picture,and that taking any single approach is unlikely to lead to productive understanding.      Susan H.Foster-Cohen is Head of the Department of English at the University of London, The British lnstitute in paris,France.