This dissertation focuses on heritage speakers - bilinguals who grow up speaking two languages: the language of their family, or the heritage language, and the main language of the larger society, or the majority language. We examine the majority language English of German, Greek, Russian and Turkish HSs in the USA and compare it to the English of monolingually-raised English speakers. The main conclusions are that heritage speakers exhibit a significant number of similarities in their majority English compared to monolingually-raised English speakers. The few observed differences do not point to qualitative shifts in the use of English by heritage speakers, but rather to slight quantitative dissimilarities in the frequencies of selected phenomena across registers. Overall, we concluded that heritage language maintenance did not have long-term negative consequences for the majority language of heritage speakers in our sample.