The armour worn by Grey Knights is archaic and baroque, anointed and inscribed with prayers and hexagrammic wards, ritually consecrated and psychically charged to do battle with the unholy. In conjunction with the psychic might of the Knights themselves, these hallowed suits of armour enable the Knights to resist their otherworldly foes. Aegis suits render the following advantages to Grey Knights:
Every time an enemy psyker uses a power that targets a Grey Knight squad or character and requires a Psychic test, that unit can resist it by rolling a D6 and adding the highest Leadership value in the Grey Knight squad. The enemy psyker must roll equal to or higher on a D6 plus their own Leadership characteristic to penetrate the Grey Knights' defences. If the psyker rolls under the Grey Knights' total the power fails. Note that the Daemonhunters player can use either this power or a psychic hood on an enemy psychic power, not both.
Minor psychic powers used by the enemy have no effect at all on Grey Knights.
Errata — Chapter Approved: Codex: Daemonhunters Q&A (v1.0): For the purposes of the Aegis, the Grey Knights Dreadnought's Leadership is considered to be 10.