The Monster Manual (MM) is the primary bestiary sourcebook for monsters in the Dungeons & Dragons (D&D) fantasy role-playing game, first published in 1977 by TSR. The Monster Manual was the first hardcover D&D book and includes monsters derived from mythology and folklore, as well as creatures created specifically for D&D. Creature descriptions include game-specific statistics (such as the monster's level or number of hit dice), a brief description of its habits and habitats, and typically an image of the creature. Along with the Player's Handbook and Dungeon Master's Guide, the Monster Manual is one of the three "core rulebooks" in most editions of the D&D game. As such, new editions of the Monster Manual have been released for each edition of D&D. Due to the level of detail and illustration included in the 1977 release, the book was cited as a pivotal example of a new style of wargame books. Future editions would draw on various sources and act as a compendium of published monsters.

The first D&D boxed set did not have a separate Monster Manual but provided listings for monsters in Book 2: Monsters and Treasure, one of the included booklets. After the series was separated into basic and advanced games, the basic game continued to be published in level-based boxes. Monsters of the appropriate level were included in the rulebooks for the various basic game sets (the Basic, Expert, Companion, Master, and Immortal sets). These monsters were later collected in the Rules Cyclopedia, which replaced the higher-level boxed sets,and the Creature Catalogue.

Games scholar Jaroslav Švelch saw the Monster Manual modeled after "medieval bestiaries, only with more precise figures": "Whereas medieval bestiaries attempted to situate unknown creatures within what was the known system of nature, games like Dungeons & Dragons created simulated natures of their own and populated them with creatures that followed their artificial laws and conditions."

The first publication bearing the title Monster Manual was written by Gary Gygax and published in 1977 as a 108-page book. It was the first hardcover book for any D&D game and the first of the core manuals published for the new Advanced Dungeons & Dragons (AD&D) version of the game. The Monster Manual was a game supplement intended to detail the standard monsters used with AD&D. The book compiles over 350 monsters, some new and others revised from older sources such as Monsters and Treasure, Greyhawk, Blackmoor, Eldritch Wizardry, The Strategic Review and Dragon magazine. Each monster was listed in the book alphabetically with a full description and game statistics and many featured an illustration.

The cover of the original printing was illustrated by David C. Sutherland III. A softcover version of the Monster Manual was printed in the United Kingdom by Games Workshop in 1978. When the book was reprinted in 1985 it featured new cover art by Jeff Easley. The book remained relatively unchanged throughout its fifteen printings up to 1989. Minor changes during the print run included a cover art change to match a new logo and house style, and some minor corrections introduced in the 1978 printings.

The first edition Monster Manual included topless portrayals of some of its female monsters, such as the succubus, Type V demons, lamia, and sylph. The first edition was also the first appearance of the mimic.

In 1999, a paperback reprint of the first edition was released. The first edition Monster Manual was reproduced as a reprint in 2012.

Monster Manual was also reviewed by Don Turnbull who felt that "this manual deserves a place on every D&D enthusiast's bookshelf", and praised the explanatory text, stating that it "amplifies, where necessary, [the game statistics] and the result is the most comprehensive listing of D&D monsters you will find, presented in a clarity which is unfortunately all too rare in other sources." Turnbull noted some minor printing errors and felt that some of the drawings were not as good as others, but felt that the book's quality "is as high as one can reasonably expect in such a complex matter". Turnbull concluded by saying "I can do no more than heap high praise on the Monster Manual. If every DM and every player didn't buy it, I would be very surprised. It is without doubt the best thing that TSR have produced so far." Lawrence Schick, author of Heroic Worlds, commented that "As nothing is easier to design than new monsters, it has spawned a host of imitations." Games journalist David M. Ewalt commented that the "Advanced Dungeons & Dragons Monster Manual may have been a rush job, but its quality is undeniable.[...] The Monster Manual succeeded not just as a game supplement but by elevating the D&D rule book to fetish object. [...] The book became a beloved companion to a generation of gamers, something they came back to again and again."