Since it was first published in 1989, Suzanne Romaine's book has been recognised as an authoritative introduction to the sociolinguistics and psycholinguistics of bilingualism. The new edition has been completely revised to incorporate recent work in this fast developing field. Throughout the book, bilingualism is seen as both a societal and cognitive phenomenon. Professor Romaine explores various aspects of bilingual behaviour, such as code switching and language mixing, in terms of their social functions within the bilingual speech community as well as in terms of neurolinguistic organisation in the individual speaker. The author also assesses the positive and negative claims made for the effects of bilingualism on children's cognitive, social and academic development, and examines the assumptions behind various language policies and programs for bilingual children. In all this, Professor Romaine draws on her own research with Panjabi/English bilinguals in Britain, and Tok Pisin/English bilingual children in Papua New Guinea.