Recording and music
Nine Inch Nails frontman Trent Reznor announced in 2007 that the band had completed its contractual obligations to its record label, Interscope Records, and would no longer be working with the company. He also revealed that the band would likely distribute its next album independently, possibly in a fashion similar to Saul Williams' 2007 album The Inevitable Rise and Liberation of NiggyTardust!, which Reznor produced.
Following the Performance 2007 Tour in support of the band's previous album Year Zero (2007), Reznor set out to make a record "with very little forethought". Ghosts I–IV originated from an experiment: "The rules were as follows: 10 weeks, no clear agenda, no overthinking, everything driven by impulse. Whatever happens during that time gets released as ... something." Reznor explained, "I've been considering and wanting to make this kind of record for years, but by its very nature it wouldn't have made sense until this point".
The core creative team behind the project was Reznor, Atticus Ross, and Alan Moulder. Live-band member Alessandro Cortini and studio musicians Adrian Belew and Brian Viglione also contributed instrumental performances on select tracks. Reznor described the band's early intentions for the project as "an experiment", and explained the group's process: "When we started working with the music, we would generally start with a sort of visual reference that we had imagined: a place, or a setting, or a situation. And then attempt to describe that with sound and texture and melody. And treat it, in a sense, as if it were a soundtrack."
The musicians created the album tracks through improvisation and experimentation. As a result, the initial plan to release a single EP of the material expanded to include the increasing amount of material. Viglione contributed percussion to tracks 19 and 22. He stated that Reznor's instructions to him were to "build a drumkit. Piece together any stuff that you want to bang on; rent what you want to rent. Have fun and ... be creative—See where your mind and your ideas take you." Viglione's makeshift drum kit included a 50-gallon trash can, a pair of water cooler jugs, and a cookie tray with a chain across it. Alessandro Cortini is credited on a total of ten tracks from Ghosts for his contributions on guitar, bass guitar, dulcimer, and electronics. Cortini was brought onto the project two weeks into the process, and his involvement evolved from "first recording some extra parts to some tracks" and eventually into "a collaboration on [the] tracks noted in the booklet". Adrian Belew was also brought on for select instrumental contributions, but as the project evolved Reznor expanded Belew's involvement and shared writing credit with him on two tracks.
Ghosts I–IV is an almost entirely instrumental album, with only a few tracks containing sampled vocals. Reznor described the album's sound as "the result of working from a very visual perspective—dressing imagined locations and scenarios with sound and texture; a soundtrack for daydreams." PopMatters' review of the album compared its musical style to that of Brian Eno and Robert Fripp, ultimately categorizing it as "dark ambient". The review went on to describe the music as "a tonal painting, a collection of moods and not all of these moods are good ones." NPR compared the album to the music of Erik Satie and Brian Eno; Rolling Stone's review to Brian Eno, specifically the album's sound to the instrumentals of Another Green World (1975) and the rhythm collages of My Life in the Bush of Ghosts (1981). Robert Christgau also compared the album to the work of Brian Eno, summarizing Ghosts' sound as "mental wallpaper".
Ghosts I–IV features a wide assortment of musical instruments, including piano, guitar, bass, synthesizer, marimba, tambourine, banjo, dulcimer, and xylophone, many of which were sampled and distorted electronically. Percussion instruments, contributed primarily by Brian Viglione, were constructed largely out of found objects and household items.
Rob Sheridan acted as the album's art director, in collaboration with Artist in Residence. Sheridan was also art director for the previous two Nine Inch Nails studio albums, With Teeth (2005) and Year Zero. Since Ghosts was released in a variety of versions, some of the versions feature somewhat differing (or additional) album art and related artwork. A 40-page PDF comes with each version of the album and contains a photograph for each of the 36 tracks. These photographs are also embedded into the ID3 tags of every downloadable track.