Which Harry Potter book is the longest in the English editions?

Harry Potter and the Order of the Phoenix is the longest Harry Potter book in the English editions.

The fifth novel was published in 2003 and is substantially longer than the other six books in the English-language series. It follows Harry’s fifth year at Hogwarts, the return of Lord Voldemort, and the Ministry of Magic’s campaign to discredit Harry and Albus Dumbledore.

The novel introduces Dolores Umbridge as Hogwarts’ High Inquisitor and includes the formation of Dumbledore’s Army. Harry, Hermione, and Ron organize the student group so classmates can learn practical defensive magic while Umbridge restricts instruction. The book also builds toward the battle in the Department of Mysteries.

Readers sometimes assume Harry Potter and the Goblet of Fire or Harry Potter and the Deathly Hallows is the longest because both are large books and major plot turning points. Page counts vary between editions because of trim size, type, and translation, but in the original English series Order of the Phoenix is the longest by word count and commonly by page count.