The Oxbridge Solution: Returning to the Medieval Roots of Higher Education (under review)

Hobbit Virtues: Rediscovering Virtue Ethics through Tolkien (New York and London: Pegasus/Simon & Schuster, 2020)

Gatsby’s Oxford: Scott, Zelda and the American Invasion of Oxford in the Jazz Age, 1904-29 (New York: Pegasus; Toronto: Penguin/Random House, 2019); Chinese edition (Shanghai, 2025)

The Making of Middle-earth: A New Look inside the World of J.R.R. Tolkien (New York: Sterling, 2013; rev. ed. 2022); published in German (Heel Verlag, 2013)

General Editor, The Early Peoples of Britain and Ireland: An Encyclopedia, 2 vols. (Oxford and Westport, CT: Greenwood International, 2008)

The Britons, The Peoples of Europe series (Oxford: Blackwell, 2003; 2^nd printing, 2005); published in Italian (Genoa: ECIG, 2007), Chinese (Beijing: Peking Univ. Press, 2009), and Polish (2011)

The World of King Arthur (New York and London: Thames and Hudson, 2000; rev. pbk. ed. 2011); published in the UK as Exploring the World of King Arthur; published in French as À la Recherche du Roi Arthur (Paris: Le Pré aux Clercs, 2001); published in Japanese in 2002

An Age of Tyrants: Britain and the Britons, AD 400-600 (University Park, PA: Penn State University Press, 1998; Gloucester, UK: Alan Sutton, 1998)

Sub-Roman Britain (AD 400-600): A Gazetteer of Sites, British Archaeological Reports (BAR) British Series No. 247 (Oxford: Tempvs Reparatvm, 1996)