* The Complete Tolkien Companion (2006)
* Tolkien: A Biography (2013)
* The World of Tolkien's The Lord of the Rings (2014)
* The Fellowship of the Ring: A Reader's Companion (2016)
* The Two Towers: A Reader's Companion (2017)
* The Return of the King: A Reader's Companion (2018)
Articles
* "Tolkien's Mythology" (2007)
* "The Lord of the Rings: A Cultural History" (2008)
* "Tolkien and the Great War" (2014)
* "The Inklings: A Literary Fellowship" (2015)
* "The Lord of the Rings: A Guide for the Perplexed" (2016)
Other
* Editor, The J.R.R. Tolkien Encyclopedia: Scholarship and Critical Assessment (2006)
* Producer, The Lord of the Rings: The Return of the King Extended Edition DVD (2004)
* Narrator, The Hobbit audiobook (2004)
* Guest lecturer, University of Oxford (2007-2018)
* Visiting scholar, University of Leeds (2019-present)