By the thirteenth century, the bestiary was one of the most popular books available in Europe after the Bible. The bestiary was both morality play and encyclopedia. The emphasis was on morality play, since most bestiarists were monks or other Christian scholars. From their point of view, the habits of animals provided insight into how we humans should be living our lives as Christians. The Medieval Bestiary: Revised Edition is an Ars Magica supplement for player and storyguide alike. You should have this book if you plan to seek a familiar, play a shape-shifting Bjornaer, or tell stories that involve animals and fantastic beasts. The creatures described in this work are presented from a medieval point of view to help set the mood of your game. The creatures described within this bestiary are ones known to the people of Mythic Europe, the setting of Ars Magica. Thus, there are familiar animals -- horses and hounds, cats and cows -- and exotic creatures -- dragons, gryphons, and sirens. Each creature is presented with a description written by Caprea of House Bjornaer, which reflects her views as a maga and scholar in the Order of Hermes. Statistics are presented for creatures when appropriate, and are compatible with Ars Magica Fourth Edition.