The Inquisition, formally called the Holy Orders of the Emperor's Inquisition, is a secret organization that exists outside of the standard administrative hierarchy of the Imperium of Man. The Inquisition acts as the secret police force of the Imperium, hunting down any and all of the myriad threats to the stability of the God-Emperor's realm, from the corruption caused by the forces of Chaos, Heretics, mutants and rebels, to assaults from vicious alien species like the Tyranids, Orks or Drukhari.