This book presents a unique range of interdisciplinary work on questions of language development and evolution. It makes visible the significant contribution which meaning-oriented linguistics is making to debates about the origins of language - from the perspective of language evolution in the species as well as language development in the child. As well as linguistics in the systemic functional, or Hallidayan, tradition, the book offers contributions from primatology, psychiatry, sociology and education. The authors are able to address major questions of deep social significance, including: • the roles grammar in the emergence of consciousness. • the dynamics of language variation in children's development. • children's learning in and about a second language. • the significance of different ways of talking about language for school literacy development. • understanding borderline personality disorder from the perspective of language development.