Аbstract
 The purpose of the study is a biographical and historiographical review of the figure, views, ideas and scientific work of the Ukrainian diasporic scholar-historian and public figure Ivan Lysiak-Rudnytskyi. The key task is to determine the influence of the researcher and his theoretical and methodological generalizations on his contemporary and especially post-Soviet Ukrainian historical science. The methodological basis of the research was primarily the methods of historiographical analysis and source criticism. Thanks to the analysis of I. Lysyak-Rudnytskyi's scientific output and the research dedicated to him, it was possible to comprehensively characterize his contribution to Ukrainian and world historical science and determine the relevance of his research even in our time. The scientific novelty is the coverage of I. Lysiak-Rudnytskyi's participation in the work of the International Congresses of Historians, especially the 13th Congress of Historians, which took place in 1970 in Moscow. Also a supplement to the currently available description was the detailing of his work on the idea of establishing contacts and cooperation between the Ukrainian Soviet and Ukrainian-American diaspora communities of historians, to which the trip of I. Lysiak-Rudnytskyi to Kyiv at the end of August 1970 was dedicated. impressions of the scientist, which he noted in his diary. Conclusions. The unique place of I. Lysiak-Rudnytskyi in the scientific and intellectual life of the Western Ukrainian diaspora in the 1950s - 1980s is determined. Despite his not entirely successful academic career and insignificant "publishing activity", the researcher received recognition and authority in the scientific and public sphere segments of the North American establishment.