Abstract In the present chapter, first, the migration background of Turkish heritage speakers in Germany will be described. Secondly, the available literature on Turkish heritage speakers with a focus on vocabulary will be discussed. Finally, the results of a recent study on heritage speakers will be presented. The present study supports the findings of previous studies which aim to answer the question whether there is a vocabulary gap in bilinguals, such that bilinguals have smaller vocabularies than monolinguals. A deficit or gap is attested for bilinguals in a number of studies when they are compared with monolingual control groups (for a detailed overview see Thordardottir, 2011 ). However, this gap seems to be an artefact of the methodology since bilinguals use their two languages in different domains ( Grosjean, 1982, 2001 , 2015 ) and almost never develop a vocabulary in both of their languages that is comparable to monolinguals. We therefore need to include both languages in an investigation of a potential bilingual vocabulary gap. However, even when both languages are investigated, a deficit in vocabulary knowledge, especially productive vocabulary is attested in many studies (for a detailed discussion see Daller & Ongun, 2017 ). Because the literature presents somewhat inconclusive results, in this study, we wanted to test whether or not the productive vocabulary of a bilingual individual group also shows a gap when compared to monolingual controls. The present study is based on picture descriptions of 23 heritage speakers and two control groups for German ( n = 18) and Turkish ( n = 30). We take both languages into account to obtain a fine-grained picture of the bilingual proficiency of the heritage speakers in our sample. A vocabulary gap can be identified for Turkish but not for German. When the children’s total conceptual vocabulary ( Pearson, Fernández, & Oller, 1993 ) is considered, however, there is no vocabulary gap for this group of bilinguals.