The essays in this volume are divided into four sections: (1) "Ethnic Diversity and National Language," (2) "Bilingualism: Its Causes and Consequences," (3) "Models and Methods," and (4) "Language Spread: A New Direction," The first part deals with the social conditions that influence acquisition of a second language, and language diversity on the national and regional level. In addition to a discussion of the forces that determine mother-tongue shift, part two reports on a demographic analysis of bilingualism and linguistic and ethnic segregation in Montreal, and language shift in the United States and Nairobi. The third part provides formal models for measuring the role language plays in binding and separating the regions of a nation, and discusses the linkage between native language diversity and national development. The essay in part four offers some basic propositions on forces affecting language spread. (AMH)