What is the longest harry potter book?

The longest Harry Potter book is "Harry Potter and the Order of Phoenix," which has a total of 766 pages. The book was published in 2003 and is the fifth installment in the Harry Potter series. The plot follows Harry Potter and his friends as they form a secret society to fight against the return of the dark wizard Voldemort, who is gaining power and followers. The book explores themes of grief, loss, rebellion, and political corruption. It received positive reviews and won numerous awards, including the prestigious Bram Stoker Award for Best Work for Young Readers. The book was adapted into a successful film in 2007 and remains one of the most popular Harry Potter books among fans.