!! The TV show:
* BadExportForYou: Inverted - the American [=DVDs=] suffer from terrible ClumsyCopyrightCensorship, with missing music and scenes, but the full version can be found in some foreign releases. On the German DVD sets the full original audio is included even in the English tracks on some episodes, although other episodes only have correct music on the German audio track.
* CaliforniaDoubling: Though supposedly set in the U.S., the fact that ''21 Jump Street'' is shot in Canada is made by the fact that the extras/bit parts were hired locally and thus do decidedly non-US things like say "grade 3" instead of "3rd grade" and write graffiti with words ending in "-our" instead of "-or".
** The only slightly blurred "Beautiful British Columbia" license plates are also a dead giveaway. And the bus route prominently displayed in the credits: Hastings.
** When a license plate is clearly visible, it says "Beautiful Evergreen State", which is the Washington state nickname, but with the British Columbia plate design.
* DawsonCasting: By the ''cops'' inside the show.
** As well as the students, especially in later seasons.
* OutOfOrder: ''Blackout'' (to add further to the confusion, this episode is a.k.a. ''Business As Usual'') is the last episode (26) of Season 4 and the last episode character Hanson appears in - his character is next [[ChuckCunninghamSyndrome Chuck Cunninghammed]] out of existence without any set-up. Taking a look at the last episodes of Season 4 though, it becomes clear that episode 20, ''Last Chance High'', actually subtly set up his character leaving - during it, he discusses with Penhall stuff like "Aren't we getting too old for this?", "We should move on", and "[Their gag] the [=McQuaid=] brothers are dead, finito!". The episode then ends with Penhall agreeing they've grown out of this phase, and giving Hanson a big man-hug. This clearly was to be the last episode character Hanson was supposed to appear in; also evidenced if you take close notice of Hanson's hair during Season 4: it grows longer over the Season, but during the episodes of the latter half of the Season, it sometimes switches length, indicating that episodes were switched in order. In any case, the ''Blackout'' / ''Business As Usual'' episode, apparently was pushed back to the end of the Season because it was deemed controversial (dealing with high school students physically attacking their teachers at school), which explains why it is such a weird ending for the Season.
* RecycledScript: The Season 4 episode "Old Haunts in the New Age" seemed this to Season 1 episode "Worst Night of Your Life". Both are Halloween episodes; are about arson in schools; feature a character that at first seems to clearly be the offender but isn't [[note]]In Season 1, the girl that broke into school to get a tape back, and is arrested; in Season 4, the girl that had psychic visions of fires to come[[/note]]; in both, the police officers reveal their true identity pretty quickly to these respective previous suspects and then go on to work together with them to get the ''real'' arsonist; in both, religion or spirituality played a role (the 1st took place in a Catholic school, the 2nd was about spiritualism); both ended with the police officers attending a Halloween prom undercover; and a fire breaking out at that prom despite the efforts of police and the schools to prevent this; and the fire doing no physical damage to anyone, but revealing the real arsonist at the prom, who then got arrested.
* YouLookFamiliar: Two prominent examples are Jason Priestly and Lochlyn (Rick) Munro, who played different characters in multiple episodes.

!! The film:
* ActorAllusion:
** Ice Cube's verse from "Straight Outta Compton" plays as he talks to Jenko and Schmidt.
** When planning for their party, Schmidt and Jenko jokingly wonder how they are going to get alcohol, since neither one has a fake ID, a reference to ''Film/SuperBad''. Jonah Hill and Dave Franco were also high school classmates in that film too.
** When Schmidt and Jenko are being briefed on HFS, two usernames can be seen as 'Chanchan' and 'Brielar'.
** A partial example. Molly is starring in a production of ''Peter Pan''. Brie Larson had auditioned to play Wendy in the [[Film/PeterPan 2003 version]].
* DawsonCasting: Although the movie parodies this with Jonah Hill (29) and Channing Tatum (32) trying to pass for high school students, it's still played straight with the actors playing the actual high school students. Brie Larson was 22 and Dave Franco was 27, both playing 18-year-olds.
* DyeingForYourArt: Jonah Hill actually lost forty pounds for the movie, in order to be able to do some of the more physically demanding stunts.
* PlayingAgainstType:
** The directors of these films are best known for ''WesternAnimation/CloudyWithAChanceOfMeatballs'' and ''WesternAnimation/TheLEGOMovie''. Lampshaded by a TV spot for ''The LEGO Movie'', which played up that it was from the directors of ''21 Jump Street'' and ''Film/TwentyTwoJumpStreet'', then adding, "Neither of which have anything to do with this movie."
** At the time Channing Tatum was pretty solidly typecast as an action star or romantic lead. This marked his first big comedy and, along with ''Film/MagicMike'', showed that he had [[LeslieNielsenSyndrome quite a flair for it]].
* TooSoon: In the audio commentary, it is mentioned that the line "Doing cocaine with Willie Nelson's horse" was originally "Doing cocaine with Whitney Houston's niece." This was changed because of Houston's death shortly before the editing of the movie was supposed to be finished, and at the last minute they had to call the actor to come in and dub over a new line.
* WhatCouldHaveBeen: Emma Stone was considered for Molly, but she was too busy filming ''Film/TheAmazingSpiderMan''.

!! General:
* TruthInTelevision: Whether or not it was deliberately inspired by the show, using young-looking police officers undercover as high school students has ''actually been done''. Read about the real-life example of Alex Salinas [[http://abcnews.go.com/blogs/headlines/2012/03/real-life-21-jump-street-undercover-cop-returns-to-high-school/ here]].