From the back of the book:
Totally compatible with all d20 System materials, the Liber Bestiarius provides a horde of new creatures for any campaign. From the massive to the minute, from the motivated to the mindless, these beasts stalk your campaign with terrifying relentlessness!
The Book of Beasts features
A full range of creatures from demons and golems to small furry mammals and new PC races!
New feats and special abilities!
Each creature entry contains
A complete description of each monster fit, for use in any setting.
Adventure hooks providing advice on inserting the monster into your campaign.
PC suitability entries offering suggestions for adding the beast as a member of the party!
A comprehensive listing of d20 System stats
Combat strategies and inclinations, including many new special abilities