This updated and revised edition of Hamers and Blanc's successful textbook presents state of-the-art knowledge about languages in contact from individual bilinguality to societal bilingualism. The book is both multi- and interdisciplinary in approach, and analyses bilingualism at individual, interpersonal, and societal levels. Linguistic, cognitive and sociocultural aspects of bilingual development are explored, as are problems such as bilingual memory and polyglot aphasia. Hamers and Blanc analyse the relationship between culture, identity, and language behaviour in multicultural settings, as well as the communication strategies in interpersonal and intergroup relations. They also propose theoretical models of language processing and development, which are then applied to bilingual behaviour. Other topics reviewed include language shift, pidgins and creoles, language planning and bilingual education.