A hivemind consists of a swarm of smaller creatures whose individual minds have supernaturally bonded into one to become a single, collective intelligence. Hiveminds often occur in swarms that have existed for generations and that have dwelled in areas of potent magical influence, particularly areas of strong psychic magic. Over time, the swarm learns to work together in more intelligent ways to achieve its goals, and it eventually evolves a cohesive mind. Of course, this evolution can be hastened by direct intervention of potent magic (typically something on the level of a miracle or wish), or as an unintended side effect of esoteric rituals, the use or destruction of artifacts, or the deaths of powerful minds.

A hivemind swarm learns from its surroundings, which in turn shape its choices in the languages it learns and the psychic spells it develops a penchant for casting. An urban swarm may pick up Common, Dwarven, Elven, or Halfling from snippets of conversations overheard through sewer grates, whereas an underground swarm may learn Dwarven or Undercommon. A hivemind may begin to exert its psychic abilities by compelling animals or people to bring it food or protect it from larger creatures, and it slowly graduates to defending itself and actively attacking as it gains experience.