The decision to write this book was taken by a group of practising speech therapists who worked with bilingually language handi- capped children in the UK. They formed a professional interest group called the Specific Interest Group in Bilingualism because of the need felt by speech therapists to have some forum for discuss- ing the challenges posed by the assessment and treatment of the bilingually language handicapped. In these regular discussion groups it became clear that similar experiences were encountered by all speech therapists working with these client populations up and down the country. They centred on managing the linguistic diversity, the need for develop- mental language information, the need for appropriate assessment protocols, the recruitment of bilingual staff and appreciating the positive perspective of working in this field. In the UK the range of languages is extensive. Italian, Spanish, Portuguese, Greek, Turkish, Polish, Ukranian, Hong Kong Chinese, Vietnamese Chinese, Creole, Black English, Bengali, Gujerati and Panjabi cover the main ethnolinguistic groups. In the 1987 ILEA language census over 140 languages were recorded as being spoken in London.