Quidditch is a game similar to soccer but played in the air on broomsticks, and Rowling wrote the book under the pen name Kennilworthy Whisp, a wizard who claims to be a Quidditch expert. Though readers of the Harry Potter books know nothing of Kennilworthy Whisp until the publication of Quidditch Through the Ages, they were familiar with the book and with the sport itself. Harry is a Quidditch player, and he learned how to play the game by reading this very book, which was mentioned in several books in the series.

As with Fantastic Beasts and Where to Find Them, the theme of Quidditch Through the Ages seems to be simply that magic exists, based on the underlying presumption that wizards can transcend the boundaries of the mortal world. In the game of Quidditch, they fly through the air on broomsticks, a feat...