This article investigates the transmission and influence of the idea of crusade in Bohemia and Poland, pivotal in shaping East Central Europe’s religious, cultural, and political landscape during the Middle Ages. Exploring cultural exchanges, political alliances, and ecclesiastical influences, it reveals the mechanisms of this ideology’s dissemination and absorption in the Piast realm. It examines the nuanced transformation in attitudes and policies following the reception of the idea of crusade, contributing to a deeper understanding of the interplay between ideology and regional dynastic dynamics and its enduring impact on the Christian world.