Which Harry Potter film first shows the Room of Requirement?

Harry Potter and the Order of the Phoenix first shows the Room of Requirement in the Harry Potter films.

The room appears when Harry and his classmates need a secret place to practise defensive magic. Since the room provides what its users require, it becomes the headquarters of Dumbledore’s Army, an unofficial student group formed after Dolores Umbridge restricts practical Defence Against the Dark Arts lessons.

The Room of Requirement returns in later films and takes different forms according to the needs of the people using it. In the final story, it becomes connected to the Battle of Hogwarts and the search for a lost object.

The room is sometimes confused with the hidden Room of Hidden Things, which is another form of the same magical space rather than a separate Hogwarts room.