Dungeons & Dragons: Dungeon Master's Guide 5th Ed

Weave legendary stories in the world’s greatest roleplaying game.
 
All you need to run a Dungeons & Dragons game is your imagination, some dice, and this book. The Dungeon Master’s Guide teaches you how to how to run D&D adventures for your players— how to invent monsters for them to fight, mysteries for them to solve, and fantasy worlds for them to explore.