Halos (albums)
Halo numbers are a system by which official Nine Inch Nails releases are chonologically ordered. They correspond to the sequence in which the releases were made, and are named by the word "Halo", which precedes the number on the release. For example, the fifth Nine Inch Nails release, Broken, is identified with the phrase "Halo Five". Halo numbers are sometimes modified for alternate versions of a release, such as the multiple releases of The Downward Spiral. Promotional-only releases do not have their own Halo numbers, although the promotional singles for "Piggy" and "Hurt" were both labeled as "Halo Ten," a title later officially used for Further Down the Spiral. A U.S. promo for "Into the Void" is mislabeled as Halo 16 because this number actually belongs to the Things Falling Apart remix album.
Pretty Hate Machine era (1989–1990)
Halo 1: "Down in It" (1989)
Halo 2: Pretty Hate Machine (1989)
Halo 3: "Head Like a Hole" (1990)
Halo 4: "Sin" (1990)
Broken era (1992–1993)
Halo 5: Broken (1992)
Halo 6: Fixed (1992)
The Downward Spiral era (1994–1997)
Halo 7: "March of the Pigs" (1994)
Halo 8: The Downward Spiral (1994)
Halo 9: "Closer" (1994)
Halo 10: Further Down the Spiral (1995)
Halo 11: "The Perfect Drug" (1997)
Halo 12: Closure (1997)
The Fragile era (1999–2002)
Halo 13: "The Day the World Went Away" (1999)
Halo 14: The Fragile (1999)
Halo 15: "We're in This Together" (1999)
Halo 16: Things Falling Apart (2000)
Halo 17: And All That Could Have Been (2002)
With Teeth era (2005–2007)
Halo 18: "The Hand That Feeds" (2005)
Halo 19: With Teeth (2005)
Halo 20: "Only" (2005)
Halo 21: "Every Day Is Exactly the Same" (2006)
Halo 22: Beside You in Time (2007)
Year Zero era (2007)
Halo 23: "Survivalism"
Halo 24: Year Zero
Halo 25: Year Zero Remixed
Ghosts era (2008)
The Slip era (2008)