Ancient Celtic Festivals and How We Celebrate Them Today (with Clare Walker Leslie), Inner Traditions, 2000
Ancient Egyptian Symbols: 50 New Discoveries: Abridged Edition (with Barbara Demeter), Done Yesterday Press, 2016
Art & Empire: Politics Of Ethnicity In U.S. Capitol 1815-1860 (Perspective On Art & Architect), Ohio University Press, 2001
Atlantis – The Andes Solution: The Discovery of South America as the Legendary Continent of Atlantis / St. Martin’s Press, 1998
Atlantis and 2012: The Science of the Lost Civilization and the Prophecies of the Maya, Bear & Co., 2010
Atlantis in America: Navigators of the Ancient World (with Ivar Zapp), Adventures Unlimited Press, 1998
Atlantis in the Amazon: Lost Technologies and the secrets of the Crespi Treasure, Inner Traditions, 2011