From the back of the book:
The Illithiad is a visually stunning tome that details important information in mind flayers, their mental powers, and their dire plans to control the multiverse.
This "complete book of illithids" covers:
The anatomy and physiology of the mind flayer.
The terrible truth about the mind flayer life cycle.
Illithid-kin, undead mind flayers, and new 'flayer-kin monsters.
A balanced look at illithid psionic powers.
Illithid origins, history, theology, psychology, and society.
A detailed description of a typical mind flayer community.
Unique mind flayer psionic abilities and items.
The Illithiad is the third volume in the popular MONSTROUS ARCANA™ game accessory series and is indispensable to DMs who want to add terrifying creatures to their campaigns. The Illithiad supports the mind flayer adventure trilogy: A Darkness Gathering, Masters of Eternal Night, and Dawn of the Overmind.