This study concentrates on the Hellenistic and Roman periods in the history of Greek language. It focuses on the gradual contamination of classical dialects by the Hellenistic Koine, their disappearance, the range of intraregional variation, and the process of Koinization from the angle of interregional adjustments. The author draws on recent sociolinguistic methods dealing with lexical and social diffusion of linguistic change, statistical analysis, and research into bilingualism and diglossia.