Soul-Binding is the ritual which protects and strengthens the soul of a human psyker who shows the potential to become an Astropath or other Sanctioned Psyker of the Imperium of Man, by combining a tiny portion of the Emperor of Mankind's own immeasurable willpower and psychic strength with his or her own. This agonising ritual is a brutal but necessary evil, for the daemons of the Warp have an insatiable lust for using the minds of mortal psykers as gateways into realspace from which they can wreak their terror and destruction. Fortunately, daemons cannot exist for long in the material universe, needing to find psychic gateways to possess in order to leave the Warp. Such gateways, though rare, do exist. The most vulnerable portals are the souls of psykers, whose powers open up a path between reality and the Warp, a path that a daemon may discover and follow to possess the mind and body of the psyker. Soul-Binding is necessary to gird the psyker's soul against the predations of the Warp and provide the discipline required to use their powers effectively without endangering others.
During this ritual process, some of the Emperor's own vast psychic energy is transferred to the psyker, which will enable them to transmit messages instantaneously over vast interstellar distances through the Warp if they are Astropaths or wield their powers with the discipline required to prevent daemons and other Warp entities from possessing their minds if they are another type of Sanctioned Psyker like an Imperial Guard Primaris Psyker or a psychic Inquisitor. This transference of energy is traumatic for the psyker -- not all survive this painful process, despite standard years of ritual preparation, and not all those that survive retain their sanity. Even many of the survivors, usually those of weaker ability, often suffer severe physical damage to the sensitive optic nerves of the eyes -- for instance, almost all Astropaths are blind. But the increased psychic abilities acquired through this ritual process are greatly enhanced, making up for this loss of sight, so that such affected psykers do not appear blind and their condition is only obvious due to their sunken and empty eye sockets. The intensity of this arcane ritual tends to overload the psyker's sensory organs, resulting in their suffering of further nerve damage, incurring a possible loss of smell, touch, or hearing as well.
According to ancient legend, the first psyker to have undergone the ritual of Soul-Binding was none other than Malcador the Sigillite, the Emperor's most trusted confidant, advisor and the Regent of Terra, who became forever psychically linked to the Emperor of Mankind.
- Codex Imperialis (1st Edition), pp. 36-37
- Rogue Trader Core Rulebook (RPG), pp. 48, 154, 158, 162-167, 168-170, 171-172
- Warhammer 40,000: Rogue Trader (1st Edition), pp. 133, 147-148
- Warhammer 40,000 Rulebook (5th Edition), pp. 104, 124
- Warhammer 40,000 Rulebook (4th Edition), pp. 94, 123