History AdaptationExplanationExtrication / HarryPotter

* ''Film/HarryPotterAndThePhilosophersStone'':
** Hagrid arrives with toddler Harry in a flying bike. In the book, it was Sirius Black, who lent him his bike to carry Harry to Dumbledore. In the film, this detail is omitted.

** In the first book, the Dursleys realize that the people at Hogwarts know that Harry lives in the cupboard under the stairs. Convinced they will be able to fool Hogwarts by moving him to a different location, they decide to give him Dudley's spare bedroom. Since the first movie omits that detail, they never explain why Uncle Vernon and Aunt Petunia would agree to give him an actual bedroom to sleep in other than "out of the goodness of their hearts."

** The movie cuts out any mention of Veela, including Fleur's grandmother. However, it leaves in Ron spontaneously and embarrassingly asking her to the Yule Ball, making it seem like a random moment of teenage boy stupidity, instead of him being accidentally struck by her charm powers.

** In the seventh film, the question Lupin asks Harry to make sure he's not an impostor (what creature was in his office when Harry first visited) doesn't really make sense since Harry isn't shown in Lupin's office until the very end of the [[Film/HarryPotterAndThePrisonerOfAzkaban third film]], where they otherwise spend all their scenes together in places outside the office. Of course, it might still have happened offscreen.

** An arguably important line is left out of the movie. When Prof. Quarrel reveals Snape had saved Harry's life at one point, Harry is confused, saying he thought Snape hated him. Quarrel replies, "Oh, yes, Snape hates you, but that doesn't mean he wants you ''dead''."

** It's never explained exactly how Sirius supposedly betrayed the Potters to Voldemort, making him indirectly responsible for their murder. The book elaborates that they cast the fidelius charm, whereby a secret is made in principle unknowable unless the designated steward chooses to reveal it. In this case the Potters went into hiding by making Sirius the secret keeper for their location, which erased all evidence of their existence to everyone else, but Sirius later made Pettigrew the secret keeper in his stead so as to make any attempt by Voldemort to pursue him for this information futile.

** In the book, it was explained that the Dementors guarding the school grounds could see through Harry's invisibility cloak, thereby justifying his need of the Marauders' Map in order to sneak into Hogsmeade through a hidden tunnel. Since the movie leaves this fact about the dementors out, there doesn't seem to be a substantial reason why the cloak alone wouldn't have sufficed, apart from a brief gag where Fred and George catch Harry trying to sneak out with it due to the footprints he's leaving in the snow.

** The details of Percy's defection for the ministry is limited to a few appearances without dialogue.

** In the book, Harry tries to hide his identity by giving his name to the Snatchers as "Dudley". The Snatchers assume that's his surname, so Harry thinks up "Vernon" as his first name, hence "Vernon Dudley." In the movie, he simply gives his name as "Dudley. Vernon Dudley." with no further prompting in between the two.

** It's never explained exactly how Sirius supposedly betrayed the Potters' to Voldemort, making him indirectly responsible for their murder. The book elaborates that they cast the fidelius charm, whereby a secret is made in principle unknowable unless the designated steward chooses to reveal it. In this case the Potters went into hiding by making Sirius the secret keeper for their location, which erased all evidence of their existence to everyone else, but Sirius later made Pettigrew the secret keeper in his stead so as to make any attempt by Voldemort to pursue him for this information futile.

** The movie also never explains how Sirius Black escaped from Azkaban or how he knew where to find Peter once he had. In the book, he caught a glimpse of Peter's Animagus form in a newspaper photo that Cornelius Fudge had on him during a prison visit; this was what gave him enough willpower to assume his Animagus form and attempt an escape, and his less-complex thoughts as a dog kept the dementors from sensing him.

** In the seventh film, the question Lupin asks Harry to make sure he's not an impostor (what creature was in his office when Harry first visited) doesn't really make sense since Harry isn't shown in Lupin's office until the very end of the [[Film/HarryPotterAndThePrisonerOfAzkaban third film]], where they otherwise spend all their scenes together in places outside the office.

** The movie adaptation doesn't explain that the Marauders were James Potter, Remus Lupin, Sirius Black, and Peter Pettigrew, given nicknames based on their Animagus transformations. This makes Sirius and Remus's knowledge of the map later in the film seem inexplicable. Later films rectify this by having Peter consistently referred to as Wormtail, and Sirius occasionally by his nickname, Padfoot, potentially remedying the issue for confused yet observant viewers.
** While the Animagus forms of Sirius and Peter (a dog and rat, respectively) and Remus's lycanthropy are all revealed and featured prominently in the movie, James's ability to transform into a stag is never mentioned, causing Harry's stag Patronus to lack the significance it had in the book. This also makes the connection to the Marauders even more of a stretch, as there's no other reason to tie the "Prongs" nickname to James.

** Dumbledore's backstory is broadly hinted at -- it's said that his father killed some Muggles, he was once friends with Grindelwald, and he has a brother who isn't very fond of him and a sister who died young -- but it's never explained how any of these events tie together. By extension, the film leaves out an explanation of events from ''Half-Blood Prince'', specifically Dumbledore's reaction to drinking the potion on the journey to recover Slytherin's locket, which Harry recognized in hindsight was due to him reliving the events that led to his sister's death. It was this realization that led to Harry's and Aberforth's faith in Albus being restored, whereas in the movie Harry's wavering trust in him never comes up and Aberforth's is seemingly resolved on its own and without incident. Somewhat rectified by the ''Film/FantasticBeasts'' films, which have a younger Dumbledore mention the loss of his sister to another character with the implication that later installments will explore this more. Aberforth has also been cast for the upcoming third film.

** In the first book, the Dursleys realize that the people at Hogwarts know that Harry lives in the cupboard under the stairs. Convinced they will be able to fool Hogwarts by moving him to a different location, they decide to give him Dudley's spare bedroom. Since the first movie omits that detail, they never explain why Uncle Vernon and Aunt Petunia would agree to give him an actual bedroom to sleep in.

** In the first book, the Dursleys realize that the people at Hogwarts know that Harry lives in the cupboard under the stairs. Convinced they will be able to fool Hogwarts by moving him to a different location, they decide to give him Dudley's spare bedroom. Since the first movie omits that detail, they never explain why Uncle Vernon and Aunt Petunia would agree to give him an actual bedroom to sleep in other than "[[BlatantLies out of the goodness of their hearts]]."

** Several scenes which explained Voldemort's background are missing, in particular, the scene where Dumbledore explains what the Horcruxes might be, making the nature of the Horcruxes in the subsequent movies seem much more random. In the following films (most notably when Harry searches for Hufflepuff's cup), Harry has a sort of "Horcrux-sense" (presumably from [[spoiler:his holding a Horcrux within his body]]) that helps him find the unknown Horcruxes. There also isn't a lot of explanation to why Dumbledore [[spoiler:knew a Horcrux would be lurking in that cave in the ''Half-Blood Prince'' film. Yes, a photo of the very cave is seen in Tom Riddle's childhood, thus why Dumbledore would logically suspect its correct hiding place, but it's easy to miss and the "field trip" is not touched upon.]]

* Remus and Tonks have a blink-and-you-miss-it scene where Tonks is apparently about to announce her pregnancy, but is interrupted. Their relationship is not mentioned again, until a scene late into in ''Deathly Hallows Part 2'' when Harry is aware of their son Teddy's existence, despite it not being established before.

** The shard of the mirror Harry uses to communicate with Aberforth Dumbledore is a slightly odd example -- it was originally given to Harry by Sirius in ''Order of the Phoenix'', in a scene that was left out of that film adaptation, and yet he suddenly has it at the beginning of ''Deathly Hallows Part 1''. ''Part 2'' does explain that Aberforth's mirror was bought from Mundungus Fletcher, who stole it from Sirius's house, as in the book, but there's still no explanation of where Harry's shard came from. Harry, though he'd never officially met him, knew about Aberforth since the middle of the fourth book but straight up says to Elphias Dodge he didn't know Dumbledore had a brother in the movie.
** Remus and Tonks have a blink-and-you-miss-it scene where Tonks is apparently about to announce her pregnancy, but is interrupted. Their relationship is not mentioned again, until a scene late into in ''Deathly Hallows Part 2'' when Harry is aware of their son Teddy's existence, despite it not being established before.

*** Alternatively, it is possible that the filmmakers were attempting to omit this particular plot point altogether, and that Voldemort's failed attempt to kill Harry with Malfoy's wand was merely intended as {{Foreshadowing}} of his later failure to use the elder wand without also earning its "approval."

** While the Animagus forms of Sirius and Peter (a dog and rat, respectively) and Remus's lycanthropy are all revealed and featured prominently in the movie, James's ability to transform into a stag is never mentioned, causing Harry's stag Patronus to lack the significance it had in the book.

** Dumbledore's backstory is broadly hinted at -- it's said that his father killed some Muggles, he was once friends with Grindelwald, and he has a brother who isn't very fond of him and a sister who died young -- but it's never explained how any of these events tie together. By extension, the film leaves out an explanation of events from ''Half-Blood Prince'', specifically Dumbledore's reaction to drinking the potion on the journey to recover Slytherin's locket, which Harry recognized in hindsight was due to him reliving the events that led to his sister's death. It was this realization that led to Harry's and Aberforth's faith in Albus being restored, whereas in the movie Harry's wavering trust in him never comes up and Aberforth's is seemingly resolved on its own and without incident. Somewhat rectified by the ''Film/FantasticBeasts'' films, which have a younger Dumbledore mention the loss of his sister to another character with the implication that later installments will explore this more.

** Without the book's explanation that he's secretly a Squib -- [[MuggleBornOfMages descended from a magical family, but unable to do magic himself]] -- it's left a mystery why Filch's cat, of all things, would be the basilisk's first victim in the movie, nor should he have had an immediate reason to think Harry was responsible. The scene establishing Filch as a Squib was originally filmed, but ended up being cut from the final product.

** The shard of the mirror Harry uses to communicate with Aberforth Dumbledore is a slightly odd example -- it was originally given to Harry by Sirius in ''Order of the Phoenix'', in a scene that was left out of that film adaptation, and yet he suddenly has it at the beginning of ''Deathly Hallows Part 1''. ''Part 2'' does explain that Aberforth's mirror was bought from Mundungus Fletcher, who stole it from Sirius's house, as in the book, but there's still no explanation of where Harry's shard came from.

** While the animal forms of Sirius and Peter (a dog and rat, respectively) and Remus's lycanthropy are all revealed and featured prominently in the movie, James's ability to transform into a stag is never mentioned, causing Harry's stag Patronus to lack the significance it had in the book.
** The movie also never explains how Sirius Black escaped from Azkaban or how he knew where to find Peter once he had. In the book, he caught a glimpse of Scabbers in a newspaper photo that a visitor to the prison had on him; this was what gave him enough willpower to assume his animal form and attempt an escape, and his less-complex thoughts as a dog kept the dementors from sensing him.

** In the book, it was explained that the dementors guarding the school grounds could see through Harry's invisibility cloak, thereby justifying his need of the Marauders' Map in order to sneak into Hogsmeade through a hidden tunnel. Since the movie leaves this fact about the dementors out, there doesn't seem to be a substantial reason why the cloak alone wouldn't have sufficed, apart from a brief gag where Fred and George catch Harry trying to sneak out with it due to the footsprints he's leaving in the snow.

** This trope is straddled with a little regarding the Deathly Hallows themselves. In the movie, the Elder Wand and the Resurrection Stone play the same roles they did in the book, but it's never clarified that Harry's Invisibility Cloak is the same one featured in the legend, and that Harry is descended from the third Peverell brother. However, the existence of other Invisibility Cloaks and what sets Harry's apart from them (that being, his cloak never faded over time like the other ones did) was also omitted during the adaptation process of the books. Therefore, there remains the ''implication'' that Harry's cloak is the same one from the legend, by virtue of it being the only one seen or mentioned in the films' continuity.

The ''Film/HarryPotter'' films are full of AdaptationExplanationExtrication. One major reason why the series is so guilty of this is that the book series was still ongoing while the films were being made, so the scriptwriters had no idea what bits might provide pertinent background for future events. Another reason is that, with the books becoming longer and more intricate, it simply left the films with less and less room to fill in certain background details. The first two films are about as close to word for word adaptions as one can get but things started getting cut in spades with the third.

The ''Film/HarryPotter'' films are full of AdaptationExplanationExtrication. One major reason why the series is so guilty of this is that the book series was still ongoing while the films were being made, so the scriptwriters had no idea what bits might provide pertinent background for future events. Another reason is that, with the books becoming longer and more intricate, it simply left the films with less and less room to fill in certain background details.

** The movie adaptation doesn't explain that the Marauders were James Potter, Remus Lupin, Sirius Black, and Peter Pettigrew, given nicknames based on their Animagus transformations. This makes Sirius and Remus's knowledge of the map later in the film seem inexplicable. Later films rectify this by having Peter consistently referred to as Wormtail, and Sirius occasionally by his nickname, Padfoot, potentially remedying the issue for confused viewers.