Słowa kluczowe: Polish Kingdom, Ladislaus Jagiello, monarchy, legitimization of power, royal advisors, general assemblies, monarch, vassal, Witold Kiejstutowicz, Grand Duke of Lithuania, Poland’s union with Lithuania, Byzantine-Russian paintings, cathedral in Sandomierz, Anna of Cilli, Ladislaus Ja­giello, church union, Ladislaus Jagiello, grand duke Witold, Union of Horodło, succession to the throne, archbishop Mikołaj Trąba, heraldic adoption, Union documents, The Polish Church, synodal legislation, preaching, parish network, Queen Hedwig, Ladislaus Jagiello, Polish Kingdom, Grand Duchy of Lithuania, Ladislaus Jagiello, Catholic Church, Catholicization, church foundations, Grand Duchy of Lithuania, Jan Olbracht, Aleksander Jagiellon, union negotiations, notary instruments, Crown lords, Lublin Seym of 1569, Polish-Lithuanian Union, Crown deputies, parliamentary debate, Polish-Lithuanian federation, struggle of political factions, Catholic confessionalization, Vasa dynasty, historical memory, Polish-Lithuanian union, national identity, union tradition, comparative research on empires, historical culture of the interwar Lithuania, Kazys Pakštas, Vytautas Alantas, Antanas Smetona, Gintaras Beresnevičius, Polish-Lithuanian union, historical memory, Jagiellon policy, collective identity, provincial gentry, union of Poland and Lithuania, clerical career, heraldic adoption, participants of the Horodło convention, endowment, benefice, latifundium, boyars, Zmudz, feudalism, Council of Constance, Jagiellon monarchy, doctrinal and legal process, Christianization of Zmudz, church union, Teutonic Order, Kingdom of Poland, court of arbitration, diplomatic negotiations, subarbiter Benedict Makrai, Kingdom of Poland, Hussite movement, Czech Crown, Venceslaus IV, the university, Czech-Polish alliance, Grand Duchy of Lithuania, charters, annals, Polish-Lithuanian union