From the back cover:
The Mentalism Companion explores the magic that is mastered by the sheer power of your mind. In this book, you will find new professions, variant rules, new options, and (of course) lots of stuff for Mentalism spell users.
Here is what you will find inside...
Four new professions that use the realm of Mentalism: the Seer, the Astrologer, the Enchanter, and the Armsmaster.
More than a dozen new training packages for characters to develop.
In-depth rules and an analysis of diviniation and its effect on role playing games.
New rules for handling "mental" combat as well as new rules for handling spells that require concentration.
A discussion about the differences between the new "mental" illusions and the traditional "elemental" illusions.
Dozens of new spell lists for the realm of Mentalism.