This book charts the history of the East Slavic languages from the seventh and eighth centuries, when Slavic tribes spread across the East European Plain and encountered its non Slavic peoples. It traces how Eastern Slavic dialects and written languages developed over a millennium, shaped by shifting social and ethnic landscapes, and how these changes ultimately produced Belarusian, Russian, and Ukrainian as distinct languages. Engaging with the many contested questions in East Slavic linguistic history, the book offers a clear, well documented account supported by an extensive bibliography.