The article examines scientific visits to Eastern European countries, made by Academician Alexander Voldemarovich Peiye (1909–1985), one of the key figures in Russian geology of the second half of the 20th century, in the 1960s – 1980s. Peiye’s field works and findings in Albania, Bulgaria, Czechoslovakia, Yugoslavia, and Romania are analyzed. It is concluded that Peiye’s comparative studies of different regions in Eastern Europe contributed to the formation of new ideas in geotechnics and to the revision of the fixist concept that became established in Soviet geology. These works posed the question of the role of horizontal movements of Earth’s crust with renewed vigor. Peiye made a significant contribution to the development of the mobilist theory with his studies on deep faults, shear movements, tectonic delineation of the lithosphere, etc. His investigations in Eastern European countries were thus in line with the context of scientific debate between the fixists and the mobilists in Soviet geology. It is shown that Peiye’s Eastern European trips allowed him to form a wide circle of personal acquaintances among the scientists from different countries (V. Zoubek, D. N. Andrusov, J. Fülöp, A. Codarcea, and others), who provided support not only to his own research but also actively engaged in the dialogue with their Soviet colleagues. These contacts ensured the success of many international cooperation initiatives such as the creation of the problem commission “Global Correlation of Geological Phenomena” in 1973. The article is based on the materials from Peiye’s personal fonds in the Archive of the Russian Academy of Sciences and on the documents from the archives in the Czech Republic, Slovakia, Bulgaria and Serbia, all of which are introduced for scientific use for the first time.