The Mathematics of Magic is a fantasy novella written by science fiction and fantasy authors L. Sprague de Camp and Fletcher Pratt as the second story in their Harold Shea series. It was first published in the August 1940 issue of the fantasy pulp magazine Unknown. It first appeared in book form, together with the preceding novella, "The Roaring Trumpet," in the collection The Incomplete Enchanter, issued in hardcover by Henry Holt and Company in 1941, and in paperback by Pyramid Books in 1960.