The Dungeon Master's Guide (DMG or DM's Guide; in some printings, the Dungeon Masters Guide or Dungeon Master Guide) is a book of rules for the fantasy role-playing game Dungeons & Dragons. The Dungeon Master's Guide contains rules concerning the arbitration and administration of a game, and is intended for use by the game's Dungeon Master.

The Dungeon Master's Guide is a companion book to the Player's Handbook, which contains all of the basic rules of gameplay, and the Monster Manual, which is a reference book of statistics for various animals and monsters. The Player's Handbook, Dungeon Master's Guide, and Monster Manual are collectively referred to as the "core rules" of the Dungeons & Dragons game. Both the Dungeon Master's Guide and the Player's Handbook give advice, tips, and suggestions for various styles of play.

While all players, including the Dungeon Master, are expected to have at their disposal a copy of the Player's Handbook, only the Dungeon Master is expected to refer to the Dungeon Master's Guide or Monster Manual during gameplay.

The original AD&D Dungeon Masters Guide (sic) was published by TSR in 1979. It was written by Gary Gygax and published as a 232-page hardcover with a cover by David C. Sutherland III. The book was intended to provide Dungeon Masters all the information and rules necessary to run a campaign for the D&D game. The 1983 printing featured a new cover by Jeff Easley.

Like other volumes of Dungeons & Dragons handbooks, the Dungeon Masters Guide has gone through several versions through the years. The original edition was written by Gary Gygax and edited by Mike Carr, who also wrote the foreword. The original cover art was by David C. Sutherland III, and interior illustrations were provided by Sutherland, D. A. Trampier, Darlene Pekul, Will McLean, David S. LaForce, and Erol Otus.

The first edition Dungeon Masters Guide covered the essential game rules for the Dungeon Master: creating and managing both player characters and non-player characters, directing combat, and handling adventures and campaigns that last multiple sessions. The book also included game statistics for magic items and treasure, details how to use random monster encounters, and provides statistics for some of the basic monsters and creatures of the game. New magic items were introduced.

The Dungeon Masters Guide contains scores of tables and charts for figuring damage and resolving encounters in a typical adventure, tables and rules for creating characters, and lists of the various abilities of the different classes of characters.

One supplement to the Guide was the Dungeon Masters Screen: two heavy-duty tri-fold boards with the most frequently used tables printed on them for easy reference. The 1979 second edition of the screen describes its purpose as "useful for shielding maps and other game materials from the players when placed upright, and also provide[s] instant reference to the charts and tables most commonly used during play." The Advanced Dungeons & Dragons Second Edition screen came packaged with a brief adventure; later editions of that screen, and screens produced for later editions, have instead included character sheets and general reference booklets.