This chapter provides a review of the research previously conducted on Persian heritage linguistics, with a focus on the domains of phonology, morphology and syntax. The characteristics of Persian heritage speakers are compared with the competence of second language (L2) learners in Persian to identify similarities and differences between the two groups. Findings suggest that heritage speakers have a native-like competence in phonology and show strong acquisition of morphological paradigms, outperforming L2 speakers. In contrast, derivational morphemes and features that are not salient in the input have not been fully acquired in heritage language; L2 learners tend to do better than heritage speakers in these domains. In the syntactic domain, the competence of heritage speakers is subject to increased variation– overall, these speakers do not perform as well as native speakers on recognition and production of syntactic patterns, but tend to do better than L2 learners. Persian heritage speakers show strong awareness of agreement relations, argument structure and tense dependencies, but struggle with selection of functional elements, which seem to be subject to interference effects from the dominant language. These characteristics confirm findings in the field of language acquisition, suggesting that heritage language shows a preference for perceptually salient forms, overregularization of certain features, paradigm leveling, and a penchant for analytical structures.