The church and religious situation in Central and Eastern Europe in the first half of the 15th century, which changed dynamically under the influence of both foreign policy and internal church factors, was analysed. The Western Church was able to emerge from the process known to historians as the Great Schism only after the proclamation of the principle of conciliarism at the Council of Constance (the idea of reviving the ecumenical (general) councils); a single pope was elected, which meant the victory of the synodal model in governing the Latin Church. The condemnation of Jan Hus’s views as heretical at this council and his burning caused a great resonance in Czech society, and gave impetus to the development of the Hussite movement, which had a reformist religious and political character. Hussies found a response in the Kingdom of Poland.From the end of the 14th century changes in church life on the Ukrainian lands were becoming visible. Kyiv gradually lost its role as the religious centre for the Eastern Slavs. At a time when the patriarchs of Constantinople insisted on preserving the unity of the Metropolitanate of Kyiv, Grand Duke Vytautas of Lithuania did not want to subordinate his lands to the metropolitan who came under the control of the Moscow princes, so he insisted on dividing the Metropolitanate of Kyiv into Lithuanian and Moscow. He sought the ordination of Gregory Tsamblak as Metropolitan of Kyiv and All Rus.During the first decades of the 15th century in the eastern territories of the Kingdom of Poland and in the Grand Duchy of Lithuania, a network of Catholic parishes was formed, not only in cities but also in rural areas. Until 1430, all Catholic bishoprics on the Ukrainian lands were endowed with land holdings and other income.At that difficult time, the idea of the unity of the two Churches, the Western and the Eastern, did not disappear. It was argued that the unification of the Churches would make it possible to achieve the unity of the completely Christian world against the Turks. The Council of Constance launched a series of negotiations between Constantinople and the Apostolic Capital. King Wladyslaw of Poland and Duke Vytautas of Lithuania supported the idea of the unity of the Churches. Due to the threat of Turkish attacks on the Byzantine capital, a unification council proved impossible.