On the basis of a large array of archival documents and historiographical base, the activity of Klymentii Sheptytskyi as abbot of the Holy Assumption Univ Lavra is highlighted. The analysis of this suggests that the abbot Klymentii not only contributed to the restoration of the model of the convents of the Studio Charter, but thanks to the author’s messages and works became the charismatic law-maker of this model. The author found out that the monasteries of the studio, headed by the abbot Klymentii, were able to: consolidate the Ukrainian emigrants, resist the denationalization from both the Russian and Polish sides; to spread education among young people and children, which has influenced the process of education in the religious-patriotic spirit of the Eastern Galician society; to create religious and ecclesiastical periodicals and a network of monastic libraries, which played a significant role in the development of Christian and national ideas among the local population; revive sacred art, which greatly enriched the national culture; support and care for the vulnerable, including orphans, the sick and the poor. In the article it is proved that the activity of abbot Klymentii (Sheptytskyi), first, became an important factor and criterion of moral and spiritual enrichment of Ukrainians, secondly, is a clear statement that the GCC stood on the principles of Christian morality, national and cultural tolerance and upholding — religious interests of Ukrainian, and the monasteries of the Studio Charter became one of the greatest expressors, the guarantor of the realization of national and cultural interests of Ukrainians in Eastern Galicia.The paper deals with organizational principles and practical work of the «Union history archive» (UHA), its functions, ways and dynamics of additions, structure and thematic policy of archival and library funds, personnel issue. The role of UHA founder Galician Metropolitan Andrey Sheptytskyi (1865‒1944) remains an uninvestigated issue in the context of interwar archival institution studies. The research based on newly discovered primary sources and materials of Vasyl Stefanyk National Scientific Library of Ukraine in Lviv, Central State Historical Archive of Ukraine in Lviv, and State Archive of Lviv oblast. Having a set of newly discovered archival documents: 381 «books of introductions», reports on expeditions, financial receipts, etc., as well as the correspondence of Metropolitan Andrey Sheptytskyi, director and staff of UHA, a unified image of UHA in its historical development is reproduced. In particular, the main aspects of the current work of the UHA, the role of the Metropolitan and director Ivan Shendryk in coordinating the processes of acquisition, monetary evaluation, purchasing of rarities with the participation of freight forwarders O. Tsynkalovsky, B. Olkhivsky and other individuals in searching for historical (church) written and printed monuments, as well as art and archaeological exhibits; establishing contacts with residents of Volyn, Kholm, Polissya, Podlasie, as well as Lithuania, Belarus, Russia and others. One of the well-established forms of UHA acquisition has been studied — the purchasing of cultural monuments in bookstores, antique shops, «on the market» and auctions that allows tracing the dynamics of UHA acquisition. The organizational activities of Metropolitan A. Sheptytskyi and the archival research works financially provided by him in the archives of the Vatican, the Peremyshl Chapter, the Archive of Ancient Acts in Warsaw, the Ossolinski National Institution in Lviv and others institutions have been studied. The structure and thematic palette of UHA components are revealed: the archive of ancient acts (before the 1917 revolution) and the archive of new acts (from 1917), book collections, including the «archival library». The initiatives of the founder of the Union History Archive, Metropolitan Andrey Sheptytskyi, on the reorganization and inclusion of UHA funds in the archive-library complex of the «Studion» book collection as an integral part of the Byzantine library and archive are highlighted. The activity of Metropolitan Andrey Sheptytskyi in preventing the destruction of the whole layer of culture and enrichment of the national treasury of Ukraine is presented on the example of coverage of the work of UHA. Keywords: Archives, Library, Metropolitan Andrey Sheptytskyi, Book collection, Union, Historical monuments, Manuscripts.