This research studies the speech of several generations of Spanish-English bilinguals in Los Angeles, California, and of a control group of Spanish speakers in two communities in Mexico from which there is large-scale emigration to Los Angeles. Questions addressed include precisely how the Spanish of the immigrants changes under the direct influence of English and what changes are the result of internally motivated processes, what type of lexico-syntactic transfer occurs at each point across the bilingual spectrum, what types of compensation are developed in response to loss and simplification, and how changes proceed both in the linguistic and the social systems. Empirical answers to these questions are of concern not only for linguistics but for social policy and education as well. Comparison of the speech of immigrants in Los Angeles with the speech of people who stayed behind in Mexico clarifies the issue of which changes are the result of Spanish/English bilingualism and which are processes with their roots in the language of the feeder communities.