This book is a complete re-formatting of the Dungeon Master Guide for AD&D 2nd Edition, with a new layout, new art and some tweaks.
From the back cover:
Here is the essential manual for the AD&D game Dungeon Master. All the information you need to create and run thrilling, sword-and-sorcery adventures is clearly laid out in the DUNGEON MASTER GUIDE. Learn all there is to know about magical spells, hundreds of magical devices and treasures, battles, travel, experience awards, and more. This fresh, new format is your guidebook to the challenging world of the AD&D Dungeon Master!