A book of hours is a private devotional book that provided prayers for different times of the day; monks often prayed together as a community as many as seven times a day, and though a pious man or woman outside the cloister might not be able to celebrate with the church as a whole, prayer books provided guidelines for personal prayer.
That was the idea, anyway: prayer books were customizable and beautiful objects of art that were also status symbols and worked the way calendars do for us today. Usually included was a calendar of widely observed holy days (a concept from which we still have “holidays”) that could be fitted to any year, and could hold a variety of prayers that could be tailored to different events--for different times of the year, for different purposes during a church service--even for birthdays and deaths.
The Murthly Hours
The Murthly Hours are kept by the National Library of Scotland and are in a mixture of languages, including Latin, Old French, and some of the earliest recorded Scottish Gaelic. This book is from the late 13th century and has been completely scanned and placed online. This site is highly recommended.
Petites Heures du Jean de Berry
The Bibliothéque Nationale de France has provided access to a great deal of Jean of Berry’s “small” book of hours on their website. In addition to miniature paintings of each of the 12 months, there are numerous illustrations of biblical events.
Les trés riches heures du Duc de Berry
The Très Riches Heures de Duc de Berry is a 15th century example commissioned by the same duke of Berry. It is not completely integrated online but the most elaborate miniatures have been scanned and linked here.
A Hypertext Book of Hours
Though the texts and miniatures are drawn chiefly from a 16th century book, the format in which they are laid out should prove helpful to the beginner to understand how these books are laid out and exactly what they contained--in this edition, all texts are translated from the Latin (on the left side of the page) to English (right side).