What is the title of the 2001 companion book J.K. Rowling wrote about the sport of Quidditch?

J.K. Rowling’s 2001 companion book about the sport of Quidditch is Quidditch Through the Ages. The book presents the history, rules and development of the wizarding game in the style of a reference work found inside the Harry Potter universe.

It is credited to the fictional author Kennilworthy Whisp and was published alongside Fantastic Beasts and Where to Find Them as a charity release. Proceeds from the original editions supported Comic Relief, a British charity known for using comedy and entertainment to raise money for social causes.

The book explains the origins of broom games, the evolution of Quidditch equipment and the role of the Golden Snitch. Rowling wrote it as an in-world text, so it is not a conventional narrative sequel. Its companion-book format is why it is often confused with Fantastic Beasts, which is presented as a textbook by the fictional Newt Scamander.