Prayer books are crucial resources for studying medieval spirituality. Compared to Western European material, Czech prayer books have received little attention. The project focuses on various prayer books used by the Bohemian aristocracy between 1370 and 1470 and the royal court's role in their evolution. It also analyses their Bohemian specifics, including the stronger textual and visual variability, early adoption of vernacular languages (German and Czech) and the unique religious situation due to the Hussite reformation. Prayer books thus demonstrate specific forms of courtly devotion and point to the differences in doctrine between Catholics and Utraquists. The research is be centred around the Book of Hours of Wenceslas IV, an idiosyncratic manuscript with original modifications of the usual sctructure accentuating the king's patron saint. The work of the international research team will result in an English monograph that will present the Bohemian textual and visual tradition within a broad political, social and cultural context.