Which J.K. Rowling book is the longest of the seven main Harry Potter novels?

Harry Potter and the Order of the Phoenix is the longest of J.K. Rowling’s seven main Harry Potter novels.

The fifth novel was published in 2003 and contains 38 chapters. Its English editions are notably larger than the other main books, with the British adult hardback edition running to 766 pages and the American edition to 870 pages.

The story follows Harry’s return to Hogwarts during a year when the Ministry of Magic denies that Lord Voldemort has returned. Dolores Umbridge is installed as Defence Against the Dark Arts teacher, while Harry and other students form Dumbledore’s Army to practice defensive magic.

Page counts vary by edition, language, font, and format. The safe comparison is that Order of the Phoenix is generally recognized as the longest main-series novel by word count and typical English edition length, not that every physical edition has identical pagination.