In the fictional universe of Warhammer 40,000, the Eye of Terror is a massive rift where the Warp enters realspace. It came into existence along with the Chaos god Slaanesh, and signalled the end of Eldar civilization.

Within the Eye, the laws of reality are no longer law; time flows at erratic rates, and matter and energy are indistinct. Horrible creatures fly through space along Warp currents, terrorizing any creature unfortunate enough to end up inside.

The Traitor Legions use the Eye of Terror as a base, striking out at opportune, seemingly random moments. The close proximity to Chaos causes horrific, painful mutations in the manner befitting the Chaos god that represents closest what the Marines hold in their hearts; the nihilistic Death Guard, for example, worships Nurgle, Chaos God of Decay, so they spontaneously generate warts, lesions, and degenerating diseases.

The Imperial world of Cadia lies nearest to the best-known stable gateway into the Eye, so it is a guardpost, watching for Chaos incursions into realspace.

Abbandon the Despoiler led an attack through the eye of terror during a massive narrative campaign that decided the fate of Cadia and many races.