The presented monograph concerns the problem of the formation of ethnic identity of the Orthodox society of the Commonwealth and, first of all, its elite in the 1650s - 1680s. What happened in the Late Middle Ages - Early New Time, namely the formation and spread of ethnic ideas, that is, interest in one's own "national" history, reflection on various elements of culture, uniting communities of people on the basis of which future nations will arise, also affected that part of the population of the territory of the former Old Russian state, which was under the supreme jurisdiction of the Polish monarchs. A special specificity to this process, which took place within the Ukrainian educated environment, was given by the fact that there were own traditions of building identity, rooted in the Developed Middle Ages. The author explores the ideas about the ethno-national identity of the Orthodox population of the Commonwealth in the middle and third quarter of the 17th century, paying special attention to the ratio of ethnic and confessional discourses in the public consciousness of the clergy and political elite of Ukrainian lands from 1648 to 1681.