Ambient industrial is a post-industrial music genre that makes use of industrial principles such as use of anti-music, extra-musical elements and shock tactics, but wields these elements with more subtlety. Additionally, ambient industrial often has strong occultist tendencies, with a particular leaning toward Chaos Magick (the image of the Black Sun is one that comes up repeatedly in post-industrial music), often giving the music a highly ritualistic flavor.
Ambient industrial is one of several directions that post-Industrial music took on after the breakup of Throbbing Gristle (the founders of industrial as an art movement) in 1981 ended the industrial period proper. Indeed, the last material that TG recorded, at least in the studio, Journey Through a Body and In the Shadow of the Sun, was ambient industrial work and pointed to the direction that several of TG's offshoots (most notably Coil and CTI) would take.
Among the many artists who work in this area are Coil, CTI, Lab Report, Lustmord, Hafler Trio, Nocturnal Emissions, Zoviet France, PGR, Akira Yamaoka, Thomas Köner, Controlled Bleeding, Nine Inch Nails (Ghosts I-IV), early Techno Animal, Robin Rimbaud, Final and Deutsch Nepal. It is important to note, however, that many of these artists are very eclectic in their output, with much of it falling outside of ambient industrial.
A "typical" ambient industrial work (if there is a such thing) might consist of evolving dissonant harmonies of metallic drones and resonances, extreme low frequency rumbles and machine noises, perhaps supplemented by gongs, percussive rhythms, bullroarers, distorted voices and/or anything else the artist might care to sample (often processed to the point where the original sample is no longer recognizable). Entire works may be based on radio telescope recordings (Arecibo Trans-Plutonian Transmissions), the babbling of newborn babies (Nocturnal Emissions Mouths of Babes), or sounds recorded through contact microphones on telegraph wires (Alan Lamb's Primal Image).