15 titles- Myth, Symbol, and Religion in The Lord of the Rings (Baltimore, Maryland: T-K Graphics, 1973)
- Against Time's Arrow: The High Crusade of Poul Anderson (San Bernardino, California: The Borgo Press, 1978)
- Dreamrider (New York: Ace Books, 1982)
- Gordon R Dickson. Survival! (New York: Baen Books, 1984)
- Poul Anderson. Dialogue with Darkness (New York: Baen Books, 1985)
- Gordon R Dickson. Forward! (New York: Baen Books, 1985)
- Gordon R Dickson. Invaders! (New York: Baen Books, 1985)
- Gordon R Dickson. The Man the Worlds Rejected (New York: Baen Books, 1986)
- Gordon R Dickson. The Last Dream (New York: Baen Books, 1986)
- Gordon R Dickson. Mindspan (New York: Baen Books, 1986)
- A Separate Star: A Science Fiction Tribute to Rudyard Kipling (New York: Baen Books, 1989) with David A Drake
- Heads to the Storm: A Tribute to Rudyard Kipling (New York: Baen Books, 1989) with David A Drake
- Shaman (New York: Baen Books, 1989)
- The Da Vinci Hoax: Exposing the Errors in the Da Vinci Code (San Francisco, California: Ignatius Press, 2004) with Carl E Olson
- The Pied Piper of Atheism: Philip Pullman and Children's Fantasy (San Francisco, California: Ignatius Press, 2007) with Pete Vere