The book explores how bilingualism develops in childhood or later; on bilingualism's social, neurological, and psychological foundations; and on bilingualism's social and cultural consequences. It also examines the wider issues of languages in contact, both psycholinguistic and socio-political, and the applications of bilingual research to language teaching, translation and interpreting, and language planning and policy-making. Hamers and Blanc's book--a thoroughly revised and updated version of their textbook originally published in French--provides a comprehensive, critical review of current research, focusing on the need for genuinely explanatory accounts and the development of satisfactory theoretical models.