From the Publisher's website:
"The original three books (The Arduin Grimoire Vol.1, Welcome to Skull Tower (Arduin Grimoire Vol.2), and The Runes of Doom (Arduin Grimoire Vol.3)) in a new, hard cover bound set!"
All of the material from the first three Arduin Grimoires is presented under one cover, with the original art, and in larger type.
Arduin Trilogy also reprints the rules from 1980's Arduin Adventure.