The title Native Speakers, Interrupted takes inspiration from an earlier book named Language, Interrupted (McWhorter 2007). However, rather than providing a broad analysis of language change across languages with many speakers, Montrul's book specifically looks at heritage language development and change amongst three groups of heritage speakers in the United States. Montrul argues that heritage learners are ‘native speakers’ (recognised as a contentious term), whose language development is often truncated due to insufficient input, amongst other factors. Unlike most publications on heritage language, which focus purely on language loss and incomplete acquisition aspects, Montrul's book breaks fresh ground by highlighting the structural properties of heritage languages as dynamic language change across linguistic domains, sociopolitical environments, and along lifespans.

The book investigates three groups of second-generation migrant heritage learners in the United States, whose parents are native speakers of Spanish, Romanian, and Hindi. Montrul argues convincingly that the language of heritage speakers provides a ‘unique testing case’ for identifying vulnerable aspects of language in terms of diachronic change.

The book comprises ten chapters plus implications. The first two chapters discuss ‘heritage speakers as native speakers’, some of whom may be interrupted, and ‘structural changes in heritage language grammars’. In these chapters a typology of native speakers is provided, and common grammatical changes exhibited in heritage learners are illustrated and discussed. Chapters 3 and 4 then turn specifically to focus on ‘differential object marking’ (DOM), which is a grammatical phenomenon where certain objects of verbs are marked to reflect various syntactic and semiotic factors. These chapters provide syntactic accounts of DOM in Spanish, Hindi, and Romanian as well as reviewing first, second, and bilingual acquisition studies of DOM and discussing how language acquisition and language change relate. Chapter 5 describes the study's research questions, hypotheses, and methodology, which prepare readers for the study's findings. Chapters 6–8 focus on DOM in the heritage languages of Spanish (chapter 6), Hindi (chapter 7), and Romanian (chapter 8) and these findings are presented in an engaging way by summarising the linguistic situation in each case and demonstrating key results through prose, charts, and poignant drawings. Chapter 9 brings together the results from the three groups and considers linguistic and situational factors which could explain structural differences, such as sociopolitical changes. An important finding is that DOM is a vulnerable phenomenon in heritage speakers and first-generation immigrants to different degrees. Chapter 10 considers language transmission with a central argument being that in many cases heritage learners influence first-generation speakers more than the other way round.

The implications for linguistics, language change, and policies are discussed at the end of the book, including the way English is often ideologically attached to success in society, which can ‘interrupt’ the full development of native, heritage languages. Overall, the book provides not only a detailed analysis of empirical data, but it also provides important practical discussions on language policy and bilingualism. These factors make it a valuable resource for scholars interested in syntactic theory, language acquisition, language change, and multilingualism.