This chapter discusses the definition of heritage language and the sociolinguistic conditions on the language development of the speakers that are identified as belonging in such a community, by providing a comparison of different diagnostics and the contribution of those for our understanding of heritage language speakers particularly. It focuses more generally on language contact and the creation of heritage language conditions in southeastern Europe and more specifically gives a detailed description on historical facts characterizing particular populations in the case of Cyprus and the endangered, heritage Arabic variety of Sanna spoken on the island. This context is particularly interesting in that it provides very similar criteria for describing two rather different linguistic situations, diglossia and heritage languages. The chapter also provides a brief discussion on the grammar properties that characterize heritage languages by drawing data from speakers of Sanna. It contributes to the discussion of different social, cultural, and linguistic circumstances that may characterize a heritage language community.