A Book of Hours is the most common type of surviving medieval illuminated manuscript. Each Book of Hours is unique, but all contain a collection of texts, prayers, psalms along with appropriate illustrations to form a convenient reference for christian religious worship.
In its original form a Book of Hours would list the appropriate texts for each liturgical hour of the day. However over time, other useful references were often added, especially calendars of the religious and secular year along with the prayers and masses required for certain holy days.
As many Books of Hours are richly illuminated they form an important record of life in the 15th and 16th century as well as the iconography of medieval christianity.
Towards the end of the 15th century various printed version of the Book of Hours were produced, with woodcut illustrations.
The most famous Book of Hours and one of the most richly illuminated medieval manuscripts, is the Très Riches Heures painted sometime between 1412 and 1416 in France for John, duke of Berry.