Summary. The purpose of the study is to research the interpretations of the Ukrainian-Moscow treaty of 1654 in the works of Polish historians of the first half of the twentieth century; study the approaches of scientists to identify the reasons for the mutual understanding of the Ukrainian Cossacks with the tsarist authorities; analyze the peculiarities of the study by Polish scholars of the history of the relations of the Hetman’s Chancellery of B. Khmelnytsky with Moscow; consider the specifics of historians’ vision of the circumstances of concluding the agreement in Pereyaslav and Moscow as well as the course of negotiations between the parties and their implementation; study the researchers’ assessments of the significance of the Ukrainian-Moscow agreement in the history of Ukraine, Tsardom of Muscovy and the Polish-Lithuanian Commonwealth. The research methodology is based on the general scientific principles of objectivity, historicism, scientific pluralism and reliance on historical sources. General scientific (analysis, synthesis, comparison) and special-historical (historical-genetic, historical-typological, problem-chronological, historical-systemic) methods have been used in the work. The scientific novelty of the study lies in the analysis of a wide range of historiographical sources that reflect the interpretations of Polish scholars of the first half of the twentieth century history of the conclusion of the Ukrainian-Moscow treaty of 1654. The peculiarities of the historians’ approaches to the causes of the union between the Cossacks and Moscow and the circumstances of its conclusion are particularly studied. The ideological influences of historical schools and political concepts on the assessments of scholars of the Pereyaslav agreement and bereznevi statti (March articles) have been analyzed. Conclusions. Polish historians of the first half of the twentieth century considered 1654 a milestone in the fate of Ukraine and one of the most important in the history of Poland. It was from the Cossack-Moscow treaty that they deduced the beginning of the rejection of the eastern lands of the Commonwealth in favor of Russia. Scholars saw the causes of these fateful events in the significant depletion of the Ukrainian uprising. As another reason, they also pointed to the complication of the international situation of the Cossacks due to frustration with the Turkish protection and the dual role of assistance to the Crimean Khanate. Polish scholars have drawn attention to the long history of Cossack-Moscow relations since the uprisings of the first half of the seventeenth century. However, they also pointed to Moscow’s unpreparedness for the war against the Commonwealth and its indecision. In their interpretations of Cossack-Moscow relations during the national liberation war Polish historians emphasized the parties’ differing views on the terms of the union. Thus, the scholars indicated that B. Khmelnytsky understood the agreement as a military understanding directed against Poland, where there was no talk of any restriction of Ukraine’s broad autonomy. Instead, the tsarist government understood the treaty as a simple incorporation of Ukrainian lands. This, in turn, as scientists have pointed out, it has caused many sharp misunderstandings. Among the most irritating researchers named the issue of financing the Cossack register and the disagreement of the Ukrainian clergy with the attempts of the Moscow Patriarchate to absorb its church structure. Thus, in the vision of Polish historians of the first half of the twentieth century, the Ukrainian-Moscow union was perceived as hopeless and even utterly dangerous for the very existence of the Ukrainian people.