Which charity book did J.K. Rowling write about the wizarding sport Quidditch?

J.K. Rowling wrote Quidditch Through the Ages as a charity book about the wizarding sport.

The book was published in 2001 under the fictional author name Kennilworthy Whisp. It presents the history, rules, teams, equipment, and development of Quidditch in a textbook-like format, supposedly borrowed by Harry from the Hogwarts library.

It was one of two companion books published to raise money for Comic Relief, alongside Fantastic Beasts and Where to Find Them. The charity editions were designed to look like schoolbooks from the Harry Potter world.

Quidditch Through the Ages is not one of the seven main Harry Potter novels. Its fictional bibliography and humorous marginal notes make it a companion work, while its real-world charity purpose connected the Harry Potter brand to fundraising.