Taking a sociolinguistics-in-action approach, Language Matters explores the language situations in Guam, the Philippines, and Puerto Rico, three geographic areas that experienced the effect of linguistic imperialism in a historically similar timeframe and manner, but with very different results. English has all but replaced the native language of Guam, plays a significant role in the multilingual society of the Philippines, but is barely existent in the daily lives of Puerto Ricans, who are mostly monolingual Spanish speakers. Language Matters is the first book to explain why this is.

The book includes a discussion of language shift and maintenance factors, including societal bilingualism, migration, socioeconomic factors, institutional support, prestige, and threats, but also examines nationalist groups' involvement in native language maintenance and the construction of national identity. It also includes an analysis of how these factors presented themselves in Guam, the Philippines, and Puerto Rico. Some of the key factors explaining the differences between the countries include societal bilingualism and prestige, but also the role of nationalist groups associating the vernacular with national identity, and in some cases simultaneously presenting English as a threat to this identity.