Into the Pandemonium is the third studio album by Swissextreme metal band Celtic Frost, released in 1987. The album is more varied than many of Celtic Frost's past LPs, with unlikely covers (Wall of Voodoo's "Mexican Radio"), emotionally-charged love songs, the album's recurring industrial-influenced rhythmic songs of demons and destruction, traditional Frost-styled songs about dreams and fear, and a dark, classical piece with female vocals.
The album is vastly different from the band's previous work and cemented its late '80s avant-garde metal term; it is also a departure from the extreme style found on the band's previous albums, Morbid Tales and To Mega Therion that Celtic Frost had become known for. However, it does have the recurring symphonic elements found on previous albums. The album has a more classic heavy metal style within the songs with elements of industrial, classical and gothic rock, and even has a hip hop/dance-inspired rhythm in "One in Their Pride". It does have a few black metal elements remaining in Tom Warrior's vocals, though, and some thrash-influenced guitar riffs.
The track "Rex Irae" is the opening part of Celtic Frost's requiem; the third, concluding part of which, "Winter (Requiem, Chapter Three: Finale)" can be heard on 2006's Monotheist. The second part of the requiem was never released by the band.
Some of the lyrics are silently borrowed from other sources. For example, significant portions of Inner Sanctum are directly quoted from Emily Brontë poems, while the lyrics to "Tristesses de la lune" are borrowed from the poem of the same name in Charles Baudelaire's Les Fleurs du mal. The lyrics to "Sorrows of the Moon" are an English translation of the same.