The Immaterium is the parallel dimension of raw psychic energy that lies beneath the skin of the material universe. Known also as the Warp, the Empyrean, and the Sea of Souls, it is a boundless ocean of pure thought and emotion where the physical laws of time, distance, and matter hold no authority. Every hope, terror, and desire felt by a living mind ripples outward into its depths, and those ripples give the dimension its ever-shifting, storm-wracked character.
Though it touches every point in reality at once, the Immaterium is a place of constant danger. Its churning tides are home to predatory entities and to the vast malign powers born of mortal passion. Where the veil between the two dimensions grows thin, the immaterial can bleed into the physical, unleashing madness, mutation, and horror upon those unlucky enough to be near.
For all its peril, the Warp is indispensable to galactic civilisation. Starships plunge into its currents to cross the void in weeks rather than millennia, telepaths hurl messages through it across unimaginable distances, and every psyker draws power from its energies. It is at once humanity's greatest tool and its deepest curse. To learn more, see the full account of the Warp and the warp-storms that erupt from it.