!! Book YMMV:
* GeniusBonus: Talliefer was the name of a Norman jester/fool, in keeping with the book's TarotMotifs.
* TheUntwist: [[spoiler:Liana, "Rochefort" and Balkan]] were actually trying to get "The Anjou Wine" from Corso all along and knew nothing of ''The Nine Gates.'' [[spoiler:Varo Borja alone]] was responsible for the murders of Fargas and Ungern.

!!Movie YMMV:
* AlternateCharacterInterpretation:
** One theory states that Corso ''is'' Lucifer himself, and the film is about him [[AngelUnaware reawakening and rediscovering his true nature]]. Several clues pointing to this are scattered throughout the film, including Corso having a very Luciferian appearance with a goatee (Goat = the beast), and his name in the book is not "Dean Corso", but [[LouisCyphre Lucas Corso]] (even within the film, the Ceniza brothers point out the significance of the LCF initials). When [[spoiler:Balkan]] is seen laying out the engravings and reciting the words for the ritual, Corso appears overhead and lampshades "what were you expecting, an apparition?" The ending also shows that [[spoiler:in the engravings of the book, Corso is represented by a seven-headed dragon with the Girl on top of him, fitting with the Book of Revelation that mentions a seven-headed Beast (also described as a dragon) with the Whore of Babylon riding on top of it, and a widely-held interpretation of this imagery is that the Beast is Lucifer/Satan.]]
** The Girl: who ''is'' she, and what is her reason for helping Corso? The most common interpretation is that she is Lucifer/the Devil/Satan, but it's also a popular theory that she's instead an agent of the Devil such as the Whore of Babylon, given that the final engraving shows [[spoiler:her riding atop a seven-headed dragon, the description of the Beast in the Book of Revelation that the Whore of Babylon rides]]. Other theories are that she's Myth/{{Lilith}}, the mother of demons; she's a succubus who is corrupting Corso to take his soul and condemn him to Hell; or she's a witch who successfully performed the ritual of the Nine Gates in the past and has chosen Corso to join her in sharing power and immortality. It's also speculated that she's actually a ''benevolent'' force -- under the theory that by the end of the film Corso has escaped the Nine Gates, the Girl would be his guardian who protected him during in his investigation and guided him to redemption. This theory is bolstered by how Corso refers to her as a "guardian angel", and in the novel she actually claims to be a fallen angel. It's also speculated that, regardless of identity, she was initially looking to Balkan as the one to discover the secret of the Nine Gates, but after meeting Corso she turned her attention to him instead.
** [[spoiler:The Ceniza brothers removed the final engraving from their copy of ''The Nine Gates'' and replaced it with a forgery. Given that they admit there's no profit to be made in forging a book like this, what are their motivations then? The logical explanation would be that they believed in the power of the books and removed the engraving to ensure no one could complete the ritual without it, but then they also snark to Corso "even Hell has its heroes", so which side do they see themselves on? Then there's the fact that by the end of the film they've vanished and their shop is being cleared out. With all the other murders its possible they were killed too, but then why wouldn't the film just say so? The original script just makes it even more mysterious, with the workmen in the final scene claiming the brothers have been ''dead'' for years.]]
** At the film's end, [[spoiler: Did Corso complete the ritual to go to Hell and achieve ultimate immortal power? Or did he complete the ritual to be with The Girl in the underworld?]]
* BestKnownForTheFanservice:
** Everyone remembers the [[DoubleEntendre climax]] where Corso and the Girl have sex, with Emmanuelle Seigner's bare breasts and butt on full display and Johnny Depp shirtless beneath her.
** And those who don't were probably mesmerized by the preceding fully nude back shot of Lena Olin.
* EpilepticTrees: Everyone has their own theory about who the Girl is.
* EveryoneIsJesusInPurgatory: Naturally, the fact that the religious supernatural elements are not directly explained allows a lot of room for speculation on what exactly they mean, including decoding the meaning of the engravings and what the differences between the A.T. and L.C.F. versions mean. It's also speculated that since apparently only two of the nine engravings are recreated in scenes Corso encounters, the other seven ''are'' recreated in other places in the film, just in a less overt manner. Or that Corso's path through the film symbolically or literally takes him through the Nine Gates. And then there's the GainaxEnding which has all sorts of interpretations.
* SugarWiki/FunnyMoments:
** In a rather serious movie, Corso finds [[spoiler:the Devil]] reading ''Literature/HowToWinFriendsAndInfluencePeople''.
** After Boris Balkan reads the riot act to the Satan worshippers, who stand around stunned... cue one perfectly executed BOO! from Frank Langella to clear the room in terror.
* GeniusBonus: Many locations in the movie have a long history related to the Occult and Medieval conspiracy stories, such as Venice, Toledo, Sintra, and the "Cathar country" in the south of France (the burning castle is Puivert, a former Cathar fortress).
* MagnificentBastard: ''The Ninth Gate'' has the tenacious AntiHero and his amoral AloofAlly:
** Dean Corso is an unscrupulous book dealer known for swindling his clients. Assigned by occultist Boris Balkan to compare his copy of a Satanic text to the other surviving ones, Corso sniffs out the discrepancies in the engravings while ignoring the deaths clearly caused by Balkan, even that of his good friend. Deciding to covet the eldritch powers Balkan seeks, when Balkan's ritual fails and burns him alive Corso uses the complete true engravings and manages to claim ultimate power.
** The [[MysteriousWaif mysterious girl]]--likely [[{{Satan}} Lucifer]] or another supernatural being--loves Corso and wishes to make him immortal. Aiding in his quest to research the Satanic text, the girl appears seemingly at random both to save Corso from danger and subtly manipulates the villains to further her lover's knowledge of the text. Purposefully allowing for the other Satanists to kill each other, she consummates her relationship with Corso before disappearing and giving him the materials he needs to covet the book's true power, masterminding the whole plot to get all she desires.
* {{Narm}}:
** Liana Telfer's hissing and clawing at Corso is rather ridiculous and just looks silly instead of threatening.
** When Corso finds [[spoiler:the Baroness]] strangled to death, it should be a frightening scene, especially since it's obvious before he reaches the body what he's going to find... then he turns the chair around and viewers are treated to the victim's face with their tongue lolling to the side and their eyes rolled back, an over-the-top expression that wouldn't look out of place in a cartoon.