- Lincoln the Unknown by Dale Carnegie, 1993-06
- Ghost Hunt: Chilling Tales of the Unknown by Jason Hawes, Grant Wilson, 2010-09-07
- Unknown Quantity: A Real and Imaginary History of Algebra by John Derbyshire, 2007-05-29
- Journal of the Unknown Prophet by Wendy Alec, 2005-10-20
- The Unknown Craftsman: A Japanese Insight into Beauty by Soetsu Yanagi, 1990-01-15
- The "Unknown" Reality, Vol. 2: A Seth Book by Seth, Jane Roberts, 1997-01
- Leaving Unknown: A Novel by Kerry Reichs, 2010-04-01
- The Unknowns: A Mystery by Benedict Carey, 2009-04-01
- Known and Unknown: A Memoir by Donald Rumsfeld, 2011-01-25
- Unknown (Outcast Season, Book 2) by Rachel Caine, 2010-02-02
- The Unknown Black Book: The Holocaust in the German-Occupied Soviet Territories
- Traders, Guns and Money: Knowns and unknowns in the dazzling world of derivatives Revised edition (Financial Times Series) by Satyajit Das, 2010-07-17
- The Tale of the Unknown Island by Jose Saramago, 2000-10-05
- Unknown Soldier Vol. 2: Easy Kill by Joshua Dysart, 2010-03-23
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