Dungeon Masters Guide - Advanced Dungeons & Dragons, 1st edition Author:Gary Gygax "All the information you need to referee your Advanced Dungeons & Dragons is in this book."
Whether you're running a single adventure or masterminding a complete campaign, the Dungeon Masters Guide is the absolute best source for information. There's no need to guess the rules. You'll learn spells, monsters, travel, magic lists, and combat rules.