- _When Shadows Fall_ (1989)
- _The Edge of Infinity_ (1992)
- _The Crystal Empire_ (1995)
- _The Shattered World_ (1998)
- _The Dark Star_ (2001)
- _The Nemesis_ (2004)
- _The Apocalypse_ (2007)
- _Pandora's Box_ (2010)
- _Lucifer's Hammer_ (2013)
- _The Last War_ (2016)
- _The Omega Sanction_ (2019)
- _The Final Day_ (2022)
Non-Fiction:
- _Hidden History of Planet Earth: The Ancient Aliens Among Us_ (1994)
- _The Paranormal: What It Is and How to Experience It_ (1996)
- _UFOs: The Secret Evidence_ (1998)
- _Mysteries of the Ancient World_ (2000)
- _The Big Book of UFOs_ (2002)
- _Conspiracy Theories: The Secret History of the World_ (2004)
- _Legends and Myths of the Ancient World_ (2006)
- _Aliens: The Secret History_ (2008)
- _The Bible Code Prophecy_ (2011)
- _The Nostradamus Prophecies_ (2014)
- _The Book of Secrets_ (2017)
- _The World's Greatest Mysteries_ (2020)