Gene Wolfe (Starmont Reader's Guide, 29): Joan Gordon (Borgo Press, 1986, 978-0930261191; reprinted as a Special Publication of the Monterey Bay Aquarium Foundation, 2008, 978-0930261184), an annotated bibliography and criticism on Wolfe's science fiction and non-fiction writing
The Wizard Knight Companion: A Lexicon for Gene Wolfe's The Knight and The Wizard: Michael Andre-Driussi (Sirius Fiction, 2009, 978-0-9642795-3-7), a dictionary of words and names from Wolfe's Wizard Knight novels
Lexicon Urthus: Michael Andre-Druissi (Sirius Fiction, 1994, 0-9642795-9-2), a dictionary of the archaic words used by Wolfe in The Book of the New Sun
The Long and the Short of It: More Essays on the Fiction of Gene Wolfe: Robert Borski (iUniverse, Inc., 2006, 978-0-595-38645-1)
Solar Labyrinth: Exploring Gene Wolfe's "Book of the New Sun": Robert Borski (iUniverse, Inc., 2004, 978-0-595-31729-5)
Attending Daedalus: Gene Wolfe, Artifice, and the Reader: Peter Wright (Liverpool University Press, 2003, 0-85323-818-9): Study of The Book of the New Sun and The Urth of the New Sun
Shadows of the New Sun: Wolfe on Writing / Writers on Wolfe: Peter Wright (Liverpool University Press, 2007, 978-1-84631-058-4)
Strokes: John Clute (Serconia Press, 1988, 0-934933-03-0)
Gene Wolfe: An annotated bibliography and criticism on Wolfe's science fiction and non-fiction writing: Joan Gordon (Borgo Press, 2008, 0-930261-18-6)
Gate of Horn, Book of Silk: A Guide to Gene Wolfe's The Book of the Long Sun and The Book of the Short Sun: Michael Andre-Driussi (Sirius Fiction, 2012, 0-964279-55-X)
Shadows of the New Sun, an anthology of stories by other authors which are all explicitly based on Wolfe stories (TOR Books, 2013)
Between Light and Shadow: An Exploration of the Fiction of Gene Wolfe, 1951-1986: Marc Aramini (Castalia House, 2015, ASIN B011YTDGY2), a comprehensive literary analysis of Wolfe's fiction from 1951 to 1986, volume 1 of 2.