The book examines the formation and development of the main varieties of the written and oral language of Ancient Russia from the 11th to the 17th centuries. The author shows how the book and folk-spoken elements of the language interacted, the meaning of words changed, some grammatical forms were replaced by others. Excerpts from the monuments cited in the book are selected in such a way that the reader can really imagine the language of various written monuments of Ancient Russia and oral spoken language. The phenomena of the language are considered in close connection with such socio-cultural phenomena as the formation of the Old Russian state, the emergence of writing, the development of ties with the Slavic south, Byzantium, and Western Europe.