Over the past 500 years, half the known languages of the world have vanished. This comprehensive overview of the study of contracting and dying languages, composed of twenty essays, investigates the wide scope of languages currently under threat of extinction. These disappearances occur in diverse speech communities where the expanding languages are both familiar, such as English or Spanish, and less familiar, such as Swedish, Thai and Arabic. The volume concludes with a look at how research into language obsolescence may affect other aspects of linguistics and anthropology—first and second language acquisition, historical linguistics, the study of pidgins and creoles, language and social process.