Designed for use with the d20 Modern Roleplaying Game, the d20 Menace Manual presents a host of villains, monsters, and other adversaries to pit against the heroes in any modern roleplaying game. It contains extensive real-world information, including information about existing organizations such as the CIA and write-ups of well-known mythical creatures such as the yeti and sasquatch. Adversaries for all levels of play are available, as are various allies, and there is extensive information on organization and factions that heroes can either join or combat.

For fans of the Alternity system: Along with other material, the d20 Menace Manual contains organizations from Dark*Matter and aliens from Star*Drive updated and converted to the d20 Modern Roleplaying Game.