The first interdisciplinary reference publication in international practice covers the entirety of the socio-political, economic, cultural and religious life of the Old Russian state from the time of its inception (IX century) until the Mongol invasion of the mid-XIII century. About 3,000 articles written by leading experts from Russia, Ukraine and Belarus reflect modern knowledge and ideas formed on the basis of the latest archaeological, numismatic, sphragistic materials, in-depth interpretation of ancient Russian written sources, the latest research and publications of foreign sources on the history of Eastern Europe. For the first time, the foreign policy relations of Rus' with the countries of Europe and Asia are covered in detail, which makes it possible to present the Old Russian state in the broad context of the medieval world. Additional reference materials - an extensive list of references, lists of ancient Russian princes, metropolitans and bishops, cities (at the beginning of the 13th century), dated manuscripts, etc. - summarize the information in the articles. Intended for specialists in various fields of Russian history and culture, art and literature, for teachers of higher and secondary educational institutions, students and high school students, as well as everyone interested in Russian history.