The city of Montreal provides an example of how residential patterns are related to linguistic background and how linguistic pluralism is maintained under conditions of constant contact and extensive bilingualism. Residential segregation between linguistic and ethnic groups is determined by the index of dissimilarity; this index has been applied to the French and British populations and to the French-speaking and English-speaking populations in Montreal. Certain basic sociolinguistic principles become evident. The mother tongue is a far more powerful determinant of ethnic residence than is a language acquired later in life. The paramount factor influencing location is proximity to ethnic compatriots. The bilinguals in each ethnic group tend to locate in areas where their monolingual compatriots are found. The continued maintenance of the various language groups reduces the need for bilingualism. The linguistic outcome in a diverse city such as Montreal is closely intertwined with the residential pattern among language groups. (VM)