Native Speakers, Interrupted aims to advance our understanding of heritage language development and change. It is argued that heritage language speakers also qualify as potential agents of diachronic language change of the diasporic variety of their language in the language contact situation. Heritage speakers are early bilinguals born with the cognitive ability to learn two or more languages fully and indeed retain native ability in specific grammatical areas of the heritage language due to their early exposure to the language. They are native speakers because exposed to their home language from birth implicitly in a naturalistic setting, in a family environment where the language was spoken. However, insufficient input and infrequent use of the heritage language during late childhood and adolescence interrupts the healthy development of the heritage language, profoundly affecting heritage speakers’ command of specific aspects of their grammar, such as vocabulary, morphosyntax and other linguistic interfaces. What is interrupted in this case is not the language as a whole, as several have proposed, but the individual language acquisition process itself, so that specific aspects of the heritage language, in some individuals, in some languages, and under some circumstances, show significant synchronic variability.