| title | ISBN-13 (ISBN-10) | year of publication |
|---|---|---|
| An Inquirer's Guide to Christian Believing: | 978-1-59752-058-4 (1-59752-058-6) | 2005 |
| Shadows of Heaven: Religion and Fantasy in the Writing of C. S. Lewis, Charles Williams, and J. R. R. Tolkien | 978-0-8298-0197-2 (0-8298-0197-9) | 1971 |