Alfonso Cuarón was offered the chance to direct this installment in the series, but declined as he would still be working on Harry Potter and the Prisoner of Azkaban.

Mike Newell decided against the studio's original idea of adapting the extremely long book into two separate films to be released several months apart, figuring that he could cut enough of the book's bulky subplots to make a workable film. It was Alfonso Cuarón, the director of Harry Potter and the Prisoner of Azkaban, who convinced him.

Mike Newell turned down directing The Constant Gardener to direct this film.

As in the second film, full-size models were used in scenes which required teen actors to keep completely still for a lengthy period of time.

Over 3,000 girls turned up at the auditions for the role of Cho Chang

Mike Newell is the first British director the film series has had.

At least one full-scale dragon was constructed on set, which could even blow real fire.

A digital "spot removing" technique was applied in post-production to clear up some of the more severe teen skin problems, since make-up tested poorly for close-up shots in particular.

According to rumours that circulated the Internet, both Rowan Atkinson and John Malkovich were considered for the role of Lord Voldemort. Both rumors were proven to be untrue.

Rumours on the Internet of a Scottish actor being cast as Viktor Krum were halted when it was announced that, as originally planned by the producers, a Bulgarian would in fact play the part. Perhaps these rumours arose because the Bulgarian was discovered in England and not in Sofia, where there was a casting call for the part of the International Quidditch Champion. Stanislav Ianevski, a Bulgarian student living in London, has been cast in the role.

Mike Newell only received $1 million to direct (whereas Chris Columbus received $10 million plus a percentage of the gross to direct Harry Potter and the Philosopher’s Stone).

During the underwater filming Daniel Radcliffe, a couple of the cast members, and all of the underwater crew posed for a photo which he later sent out as a Christmas card with Rudolph noses and antlers Photoshopped on everyone's faces.

Safety divers swam in with scuba regulators to allow them to breathe without having to surface. These scenes were shot in a huge purpose-built tank with a blue-screen background. Daniel Radcliffe alone logged around 41 hours 38 minutes underwater during the course of filming. At one point during training he inadvertently signaled that he was drowning, sending the crew into a huge panic to bring him back up to surface.

Ray Winstone and Billy Connolly were considered for the role of Mad-Eye Moody.

Rosamund Pike was the first choice for the role of Rita Skeeter but declined.

Carole Bouquet was Mike Newell's first choice for the role of Madame Maxime but declined because Studio Canal (the studio she was contracted) refused to give permission for her to negotiate for the role. Others considered for the role were Catherine Deneuve, Audrey Tautou and Emmanuelle Seigner.

Mike Newell originally decided not to have the make-up on Ralph Fiennes to give a more scary Voldemort. But he changed his mind after seeing a minimal make-up design by Nick Dudman. To complement the make-up, Fiennes shaved his head bald as well as his armpits.

Daniel Radcliffe suffered two ear infections following the underwater filming.

The inscriptions on the Riddle's family tombstone had to be digitally changed at the last minute after fans of the books, having seen promotion stills released from the graveyard scene, pointed out that none of the Riddle names on the tombstone referred to Voldemort (a.k.a. Tom Marvolo Riddle), as the filmmakers erroneously thought, but to his dad, Tom Riddle (Sr.), his grandfather, Thomas Riddle, and his grandmother, Mary Riddle, all three of whom were killed by Tom Marvolo Riddle in 1943.

As Ron, Harry and Hermione are talking in the great hall, before George and Fred attempt to enter their names in the Goblet, Hermione is reading a book. We can't see the title, but the cover features the harlequin pattern of the UK editions of the Harry Potter novels.

John Williams passed on scoring this movie in favor of Memoirs of a Geisha.

While filming his scenes as Professor Dumbledore, Michael Gambon wore street clothes under his flimsy costume. He also kept his cigarettes tucked into his socks.

Mike Newell staged a brawl with one of the twins, both to demonstrate what he wanted for a scene between the twins, and also to undermine his own "authority figure" status ("They were calling me 'sir'!") The fight got so intense that he fractured a rib in the process.

The tune you hear the teens sing to the school song, "Hogwarts, Hogwarts, Hoggy Warty Hogwarts" was written by Mike Newell. The lyrics first appeared in the first novel, "Harry Potter and the Philosopher’s Stone". (Traditionally the song can be sung to any tune the singer happens to like.)

Stanislav Ianevski, who plays Viktor Krum, has only two lines in the entire film totaling 20 words.

The kids had around three weeks of dancing practice for the Yule-ball waltz. Daniel Radcliffe however, who appears in almost every scene of the entire film, thus had only four days. In several interviews he's given that reason for why his dancing is shown mainly from the waist up (to avoid showing his fumbling feet!).

The film's reels were shipped to cinemas under its working title "Happy Days" to deter potential pirates.

Tolga Safer was one of the finalists for the role of Viktor Krum. He was subsequently called back and instead cast as Karkaroff's aide.

In the first draft of the script, a subplot featuring the Weasley twins and Ludo Bagman, the head of the Ministry's sports department, was featured prominently. In fact, it was reported that Martin Landham was cast as Bagman. In the subsequent drafts, the subplot was dropped.

It took two days to film Ralph Fiennes's cameo.

The first task with the dragon took over 140 special effect shots.

The line Moody uses "I know stories about your father that would curl your hair" is actually a line from the book but in a different scenario: Rita Skeeter says it to Hermione about Ludo Bagman.

The first names of the parents of Tom Riddle (sr.) - Thomas and Mary, as written on the gravestone - are not mentioned in the books (but do still come from the author).

Costume designer Jany Temime considered Hermione's dress for the Yule Ball as the most important, comparing it to that of Cinderella. The design of the dress was changed several times before the designers were satisfied with the results. Emma Watson was very careful not to wear it more than necessary because she was afraid that she would wreck it.

Ralph Fiennes was not wearing any make up to cover his nose. In order to make the character scarier, film editors digitally removed it. Also, the "red, snake-like eyes" the novel describes were not added, due to the actor's thought that the expression in his eyes would provide a better idea of Lord Voldemort's insanity and malignity.

In the scene where Harry faces his second task, Mad-Eye Moody has a watch with the symbol from 28 Days Later... on it. Many people may know that Brendan Gleeson, who plays Mad-Eye Moody in this film, also starred in "28 Days Later...”.

The animated hedges in the Third Task were based on Stanley Kubrick's abandoned idea for the hedge maze chase sequence in The Shining. "The Shining" was written by Stephen King, who is an avid fan of "Harry Potter" author J.K. Rowling.

Early drafts had Ron's estranged brother Percy appearing in a key supporting role but it was written out in the final drafts. In an interview, Chris Rankin, who plays Percy, revealed that his contract of the franchise stipulates that he must appear in four films; the first three, with the option of appearing in either this movie or the next one, Harry Potter and the Order of the Phoenix. Given the fact that Percy appears much longer in the latter, he opted out of the film in favour of appearing in the next one.

First film in the series not to be dubbed into Scandinavian languages (and others alike), where dubbing for theatrical release is limited to projects primarily intended for children.

When the contestants enter the arena for the third task, the Beauxbatons girls in the audience are dancing the Macarena.

The voice heard on Frank Bryce's radio in the beginning of the film is that of director Mike Newell.

In one of the first takes of Hermione's "Cinderella moment", Emma Watson actually tripped in that fancy dress and fell down the stairs.

First film in the series not to include any scenes from a Quidditch match in Hogwarts. No Quidditch matches were mentioned in the book due to the pitch being used for the maze, this is pointed out soon after the students go back to school.

Icelandic moviegoers (particularly the younger crowd) tended to crack up unexpectedly in theaters when Rita Skeeter first introduces herself. Apparently the audience weren't expecting the pronunciation of her last name, Skeeter, to sound so close to the Icelandic verb "skíta", which happens to be a rather crude word for defecating.

Brendan Gleeson and Daniel Radcliffe were both in The Tailor of Panama, Radcliffe's first movie role.

There were three characters that had big parts in the book that were completely written out of the film. These characters were: Ludo Bagman, head of the Ministry of Magic's sports department and tournament judge; Winky: the former crouch house elf that was believed to have cast the dark mark at the Qudditch World Cup; Bertha Jorkins: a woman who was tortured by Voldemort and Wormtail to tell about the Tournament being held at Hogwarts.

The occasional tongue flick done by the character of Barty Crouch Jr. was, in fact, not in the book at all, and was improvised, on the spot, by David Tennant.

The name of "Durmstrang Institute" appears to be paying homage to the "Sturm und Drang" (translation: Storm and Stress) movement in German literature. The movement, which flourished from around 1770 to 1785, was distinguished by its theme of youthful genius in rebellion against accepted standards, much like Harry and his feelings about the wizarding world's attitude toward the Dark Lord.

David Walliams was considered for the role of Barty Crouch Jr.

In the scene with Dumbledore, Harry and the Pensieve, pay close attention to the glass cabinet Dumbledore approaches while explaining the Pensieve. In the top left corner is a 3D model of what becomes an important symbol in the final novel, Harry Potter and the Deathly Hallows.

After the second task, as Dumbledore magnifies his voice, his wand (The Elder Wand) can be seen with a white band on it that bears the mark of the Deathly Hallows.