Which Harry Potter book did J.K. Rowling publish in 2003?

J.K. Rowling published Harry Potter and the Order of the Phoenix in 2003.

The fifth Harry Potter novel was released on 21 June 2003. It follows Harry’s fifth year at Hogwarts and explores the Ministry of Magic’s refusal to accept that Lord Voldemort has returned. The Order of the Phoenix is a secret organisation formed to oppose Voldemort and protect the wizarding community.

At more than 250,000 words in its British edition, it is the longest novel in the main Harry Potter series. Its length reflects several parallel storylines, including Harry’s private lessons with Albus Dumbledore, the formation of Dumbledore’s Army, and the growth of the Ministry’s control over Hogwarts.

The film adaptation was released in 2007, directed by David Yates and starring Daniel Radcliffe as Harry.