From the back of the book:
Familiars For All Classes!
The Book of Familiars brings together a host of talented writers to bring you a new groundbreaking look at the eleven core classes. Herein we expand the horizons of familiars and have developed a fully functional, well balanced approach for each character class to gain a familiar or animal companion.
The Book of Familiars offers a whole new venue for players to expand their existing games and add unheard-of dimensions to any class. Within these pages, carefully balanced rules allow players to acquire familiars for any character class they play.