- The UFO Phenomenon (Mysteries of the Unknown) by Time-Life Books, 1988-03
- Across the Unknown by Stuart Edward White, Harwood White, 1988-10-01
- A Feast Unknown by Philip Jose Farmer, 1995-01
- CAPITALISM: THE UNKNOWN IDEAL, WITH ADDITIONAL ARTICLES BY ... by Ayn Rand, Nathaniel Branden, et all 1967
- Mysterious Lands and Peoples (Mysteries of the Unknown) by Time-Life Books, 1991-09
- Tales of Mystery and the Unknown by Robert Potter, 1976-11
- Challengers of the Unknown Must Die! by Jeph Loeb, 2004-10-01
- Contesting Tears: The Hollywood Melodrama of the Unknown Woman by Stanley Cavell, 1997-02-15
- Unknown Armies (2nd Edition) by Greg Stolze, John Tynes, 2002-07
- Hauntings (Mysteries of the Unknown)
- Alien Encounters: Mysteries of the Unknown
- Tom: The Unknown Tennesse Williams by Lyle Leverich, 1997-04-01
- Art Out of Time: Unknown Comics Visionaries, 1900-1969 by Dan Nadel, 2006-06-01
- The Dream Quest of Unknown Kadath by H. P. Lovecraft, 2010-03-19
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