From the back of the book:
The Tome of the Beast...
In every dark wood. In every dank cave. In every mountain aerie. In every watery realm, there can be found... the Beast! Fabulous or mundane, Beasts of all varieties lurk in the shadow of everyday medieval life. Many fear, some respect, and even fewer ever know the Beast, but no one knows its divine purpose. From the dumb mutt on the street to the fierce drake in the mountain, the Beast is always a creature of mystery.
The Medieval Bestiary
This resource supplement for Ars Magica (but useful for any Fantasy system) describes beasts of both legend and the mundane world. Over 100 are described in detail, providing you with a comprehensive catalog of the mundane world and mystical creatures of the time. These creatures are described just as they would be in a real "Medieval Bestiary." Each Beast is also accompanied by a complete story concept, making each more significant and real than just a "Monster."