Challenges in Charming is an advanced textbook on the subject of Charms. Its physical appearance is not described in the original novels. As its title suggests, the book focuses on particularly complex and difficult-to-master Charms that go beyond the standard curriculum for O.W.L.-level students at Hogwarts School of Witchcraft and wizardry. The book serves as a reference for advanced magical theory and practical spell-casting for some of the most intricate Charms known. The most significant piece of magic known to be detailed within its pages is the Protean Charm, a highly complex spell that links the appearance of several objects so that a change to one will be reflected on the others. The inclusion of such a spell indicates that the text covers magic that is considered exceptionally difficult by wizarding standards.
The book's primary significance in the series occurs in Harry Potter and the Order of the Phoenix. After founding Dumbledore's Army, Hermione Granger devises a secret method of communication for the group's members. She gives each member a fake Galleon and, using information she learned from Challenges in Charming, places a Protean Charm upon them. When Harry Potter set the time for the next meeting, he would alter the numbers on his coin, and the other coins would instantly change to match. Hermione explains that the Protean Charm is `N.E.W.T.`-level magic, highlighting the advanced nature of the book's content. Her successful casting of the spell greatly impresses fellow student Terry Boot, who notes that it is a very difficult piece of magic. Hermione explicitly credits her success to having read about it in Challenges in Charming. This communication method was inspired by Lord Voldemort's use of the Dark Mark to summon his Death Eaters, but served a more noble purpose for the D.A.