The central pillar of most Librariums houses its oldest available copy of the Codex Astartes, held in a stasis-plinth or protected by holo-reflection. Fury of Mars - The psyker channels the mechanical wrath of the Omnissiah into an enormous, Warp-fuelled pulse that surges forth in an invisible wave to unleash ruin upon the impure technology of the foe. In this role they form the basis of the Chapter's strategic command and control, directing fleets, coordinating mass planet-drops, and providing vital intelligence during invasions and assaults. Reforge - The psyker's mind communes with the Machine Spirit of a damaged vehicle, soothing its pain as otherworldly energies reforge its wounded hull. Avenger - The Librarian summons up the ancestors of his Chapter and shapes them into a flaming, vengeful avatar of death. The construct then billows forward to incinerate those in its path.

The aspirants and newly-implanted neophytes of all Space Marine Chapters are screened by the Chapter's Librarians for signs of psychic capability. Those who possess the potential to become a Librarian are then forced to undergo the same trials and sufferings all other Space Marine neophytes of their Chapter face, but they also have to learn to harness their powers and protect their minds from the daemonic dangers of the Warp. Within the Chapter, all Librarians hold a rank based on their level of training and their standing amongst their peers. In addition to training psychic recruits, the Chapter's Librarius is also charged with recording the history of the Chapter. Librarians hold a functionary rank, describing their role within the Librarius as well as their position within the Chapter's hierarchy. Lexicaniums, for example, are responsible for preparing reports of battle for the Chapter's records, whilst codiciers provide a strategic overview of the whole theatre of a war. After many solar decades of study and book-keeping, a Librarian will be well-versed in the history and lore of his Chapter, and both his wisdom and counsel will be highly regarded by the Masters of the Chapter. Psychic powers are the physical manifestation of a Librarian's abilities, and mark him as distinct from any other individual within a Space Marine Chapter. Librarians of Codicier rank and above make use of their psychic abilities in combat. These include the ability to project their consciousness above the battlefield so that they can get a bird's-eye view of the combat in a ritual that commences with the recitation of the Litany of Sight Beyond Sight. Doing so opens a wound on their forehead exposing their psychic Third Eye, which allows them to view locations that would normally be obscured.Space Marine Battle Psykers reappeared during the Great Crusade. The early history of the Librarians is chequered with mistrust and intrigue. Initially the Legions made no use of psykers within their ranks, however Magnus the Red, Sanguinius, and Jaghatai Khan proposed the Librarian program, allowing the Thousand Sons to train and create Librarius departments in a variety of Legions. [10] Librarians were favoured for use or have been seen within the White Scars, Night Lords, Ultramarines, Thousand Sons, Word Bearers, Salamanders, Alpha Legion, [17] Dark Angels, [15] World Eaters, [18] and Raven Guard [19] Legions. Some of the Primarchs were against using psykers in the Space Marine Legions at all, or at least within their own Legions. Legions that did not favour their use or employ them were the Iron Warriors, Space Wolves, Imperial Fists, Iron Hands, Death Guard, [17] and Emperor's Children. [16] The Rune Priests of the Space Wolves, maintain that their psychic powers derives from the animistic spirits of Fenris, rather than from the Warp. [4]

The Chief Librarian is the master of the Librarius and the keeper of his Chapter's lore, as well as a member of the guiding council of the Chapter's senior officers with encyclopedic knowledge of his Chapter, its enemies, and the Imperium. Librarians are psychically-charged Astartes who are trained to use their abilities on the field of battle, as both weapons and as precognitive tools. The Librarians use a device known as a Psychic Hood to suppress their enemies' use of psychic powers and to augment their own.

Planning and bitz hunting

Astrotelepathy - Librarians can use their gifts to send psychic messages and communications across the vastness of the void in the same manner as an Astropath. It is, however, a task that is undertaken sparingly, as like much of the rest of the Imperium’s forces Space Marines make extensive use of Astropaths, reserving their gifted battle-brothers for more vital tasks. Any Librarian can use Astrotelepathy, provided he has enough time and skill—yet sending a message across the stars is a far cry from communicating with someone on the same world or even a vessel in orbit. Lifting the Veil - Lifting the Veil is an extension of the art of Psychometry and allows a Librarian to look beyond individual psychic traces and relive the past of a place or item.