* The Sword and the Grail: Warrior Saints in Celtic Britain (1991)
* Beowulf and the Nine Worthies (1993)
* Arthur and the Knights of the Round Table (1994)
* The Grail Theme: A Casebook (1995)
* The Search for Sir Thomas Mallory (1996)
* The Secret History of the Holy Grail (1997)
* The Quest for the Holy Grail (1999)
* The Arthur of History (1999)
* The Dark Side of Camelot (2001)
* The Arthurian Trilogy: The Sword and the Grail, Arthur and the Knights of the Round Table, The Quest for the Holy Grail (2003)
* Celtic Myths and Legends (2005)
* The Complete King Arthur (2006)
* The Bloodline of the Holy Grail: The Hidden Lineage of Jesus Revealed (2007)
* The Knights Templar: History and Myth (2008)
* The History of the Holy Grail: The Legend and the Artifacts (2011)
* Glastonbury: The Cradle of Christianity (2012)
* The Da Vinci Code: Breaking the Code (2013)
Fiction:
* Death of God: A Chronicle of the Apocalypse (2009)
* The Border Reivers: A Tale of the Anglo-Scottish Border in the Late 16th Century (2011)
* The Crusader's Tale: A Story of the Crusades (2012)
* The Pilgrim's Tale: A Story of the Camino de Santiago (2013)
* The Templar's Tale: A Story of the Knights Templar (2014)
* The Druid's Tale: A Story of Ancient Britain (2015)
* The Outlaw's Tale: A Story of Robin Hood (2016)
* The Heretic's Tale: A Story of the Cathars (2017)
* The Black Death: A Chronicle of the Plague (2018)
* The Viking's Tale: A Story of the Norse Sagas (2019)