A very attractive but prim and prudish woman, who would be gorgeous if she would just take off the glasses (or not), let down her hair, and unbutton her top button (or not, even without blueshifting). However, they tend to prefer more intellectual pursuits. Sometime during the course of the season, the character will be forced to do all of these things to solve some sort of problem involving a lecherous man, but will always manage to escape the situation without sex.
Naturally, there's a segment of people who find this the reason they're hot in the first place. Possibly there's also a hope that she's deeply familiar with stuff in the 155.3 or 613.9 sections of the Dewey Decimal Classification System note For those who don't understand the reference, the Dewey Decimal Classification System is a system which serves to sort documents depending to a large hierarchy of themes linked to specific numbers; 155.3 and 613.9 are respectively sex from a psychological approach and sex from a medical approach. If you want erotic literature you'll have to go to the 808.803538 shelf. Erotic art...well, that's pretty much most of the 700s.
Contrast Scary Librarian (though they can overlap), see also Beautiful All Along. Compare Magic Librarian, which is more likely to overlap. (Sometimes, all three may overlap.) Compare Hot for Teacher. Note that the character doesn't actually have to be employed as a librarian to fit this trope, as long as they fit the physical description (glasses, skirt, hair in a bun etc.) and share the same character traits (nerdy, shy and sexy). This is also common among school teachers, especially in Westerns and Historicals.
Please note that this applies to a character, not simply any hot actor playing a librarian, for the same reason Real Life examples are not listed here. Most actors are "hot" in the first place, so it usually goes unsaid. You can have an attractive librarian without their hotness being a plot element in the work - that would not fall under "Hot Librarian".
Compare Cute Bookworm for shy, sweet characters that like to read a lot.
An eyeglass maker is showing a very attractive woman, who has selected the right glasses, who is going to now roleplay the part of the "naughty librarian." "You've had some very overdue books..."
Specifically as of 2012, Lenscrafters has an ad out featuring a Hot Librarian-looking woman staring at the camera, a knowing smile on her face, and purring "You've got a LOOOOOT of late fees, mister! Maybe someone should teach you to bring in your books on time!" Freeze frame occurs, pausing the video on the bespectacled woman smiling and a voiceover says "'The Naughty Librarian,' and other looks on sale at Lenscrafters!"
Anime and Manga
Mahou Sensei Negima! has a rare male example in Albireo Imma. In-series, the girls comment on his attractiveness, and he lives under the huge Library Island surrounded by thousands of books.
Cecilia Lacques from Claudine, who works as a librarian in the local all girls's school and catches the attention of the main character due to her beauty. And she was one of the lovers of Claudine's father, actually. It all ends in tears.
Diana Prince in Wonder Woman, whose unbuttoning is part of her transformation into the titular character.
Similarly, Barbara Gordon, secretly the first Batgirl in the Batman comics and the Batman TV show. Even as the wheelchair-bound computer hacker Oracle, she's drawn as hot with glasses, simply proving that Nerds Are Sexy.
Bonus points for being an actual librarian back when she was Batgirl.
Empowered's "much-vaunted disguise, the legendary Librarian Sexy", drawn to the hilt.
When she gets home in that issue, she's trying to brag to Thug Boy about her mission, but his POV of her outfit keeps shoving her talk bubbles out of the frame. Eventually he just grabs her and carries her to the bedroom.
When Meriem becomes a Hot Teacher in Cavewoman: Killing Dinos 101, she wears a sexy librarian outfit that she later strips off to reveal her Fur Bikini.
Twilight Sparkle from My Little Pony: Friendship Is Magic fits this trope as far as personality goes, but she's more of a Cute Librarian than a hot one. In fanart however, it's quite popular to go this route with her, especially when she's drawn as a human.
In Harry Potter and the Paradigm Shift Ron teasingly remarked that maybe Harry and Hermione could do "that Sexy Librarian fantasy" one of the guys at her new school wanted to perform with her.
In Past Lives one of Hermione's former lives was head of the Great Library of Alexandria. After Harry cast a spell (at her urging) which brought this personality to the fore, she transfigured her school uniform into a tight black leather outfit and conjured up a bullwhip.
Rachel Weisz's character from The Mummy actually is a librarian. And extremely hot. Apparently they discover contact lenses or laser surgery in the twenties, though, because she never puts the glasses back on after the first time she takes them off.
Arguably, they're reading glasses, and she doesn't need them to see other things. At least until the sequel, in which she is required to read again, and still doesn't put the glasses back on.
Fridge Brilliance for the first film. She lost all her clothes on the river boat and was forced to buy new stuff when they got to the market. A desert market is unlikely to have glasses for sale.
Also, contact lenses existed in the twenties.
Mary Bailey from It's a Wonderful Life: If her husband, George, had never been born, she never would've married and would've become a librarian (but still hot though).
Carolina (Salma Hayek), in Desperado, although she, like the entire town, acts as a mule for the Big Bad's money; the library is just a front.
Best Film Noir example: the rare-books shop girl Marlowe encounters in The Big Sleep, who whips off her glasses, lets her hair down and closes up the shop suggestively (with Marlowe still in it) at the end of her scene.
In Orange County, Jack Black's character unleashes the inner beast within prim desk clerk Mona (played by Jane Adams). She tries to stop him from breaking into the building and he suggests they start a revolution together. Later they're shown lying down, possibly having slept together, getting high. She ends up being an accessory in burning down the building (metaphorical for her inner sexuality-fire-having been lit up)
Averted in That Touch Of Mink. Roger (Gig Young) is dictating and stops in the middle to ask Miss Jones (Jan Burrell) to take off her glasses and shake her hair back. Miss Jones is very near sighted and looks around, nearly blind, with very squinty eyes looking even less attractive than with her glasses on.
A man walks into a library and asks the librarian whether he could take out some books. She says yes. He then asks if he could take her out. "Sir," she said, blushing, "We librarians are for reference only."
One of the ultimates is Elizabeth Peter's Jaqueline Kirby. She was a pre-Amelia Peabody Emerson, and though never as popular as that character ended up with probably six or seven excellent third-person mysteries to her name. She is, when she lets herself "unbutton" (i.e. takes off her glasses, lets down her hair, and...well, unbuttons her blouse) a gorgeous redhead who manages to turn men to a weak-kneed jelly and is a remarkably proficient sleuth.
Miss Christobel Charteris, the female lead from Florence Barclay's book Through the Postern Gate. Also The Ojou.
On the Discworld, Sacharissa Cripslock (introduced in The Truth) was a prim and severely-dressed young woman who impressed her new boss, newspaper editor William de Worde, as no more than average-looking. However, he eventually realised that she was in fact stunningly beautiful if considered over several centuries - the equivalent of a Renaissance face, pre-Raphaelite eyes, Classical figure and, for some reason, "good medieval ears". And that as just her face; her body featured "a well crafted supply of other features that never go out of fashion at all", and for some reason she seemed to think that wearing extremely plain dresses would downplay this fact.
In the Wild Cards series, Jennifer Malloy, also known as the elite thief Wraith, almost qualifies. She's a very attractive blond, a librarian in the New York Public Library's rare books collection, dresses down and puts her hair up as a librarian (as Wraith she wears a black string bikini, a mask and ballet slippers)... but I don't think she wears glasses.
Lirael, from the Old Kingdom books, may not wear glasses, and hides behind her hair rather than keeping it tied back, but it's implied that she's good looking at several points, and she is actually a librarian, specifically, a second assistant librarian in the great library of the Clayr, which is filled with all sorts of dangerous things, as well as books.
Live Action TV
Jill Taylor in Home Improvement. In one episode, she and her husband debate whether she can succeed in a job interview without being good-looking. She puts her hair up in a bun and goes for the "librarian look" and Tim admits that he's more attracted to her than ever.
Subverted with Kitty on Arrested Development: after GOB tells her to take off her glasses and let her hair down, he shrieks at her ugliness/crosseyedness and requests she undoes them. Later, he tries various combinations of these, to no avail.
Of course, all efforts to make her look ugly aside, Judy Greer, who plays Kitty, is actually very attractive.
An episode, "Page Turner" of CSI: NY featured a fairly attractive librarian. She was, however, "hot" for another reason - she'd been murdered with radioactive Thallium 201.
In the first episode of Dollhouse, Eliza Dushku puts her hair up, wears severe clothes and glasses, and looks completely different. Still hot, but completely different. (She's actually a negotiator, not a librarian.)
Also Bennettalthough with a side of Ax-Crazy. It's even lampshaded by Topher.
Joanna Frankel, one of the Power Trio on Eastwick, has a habit of looking up from under her ridiculously hot glasses.
In the Seinfeld episode "The Library", Kramer hooks up with a fetching librarian: "...she needs a little tenderness. She needs a little understanding. She needs a little ''Kramer''."
"Yeah, and then she's gonna need a little penicillin!"
in the 1972 ABC TV movie Second Chance, the 1960s sex symbol Juliet Prowse played teacher Martha Foster, who didn't exactly look like the prim and proper frontier teacher heroine Geoff Smith (played by tough guy actor Brian Keith) was expecting to find.
Tara Carlisle, the attorney of one of the Leverage team's clients, is obviously not a librarian, but she still sort of fits this trope (enough that on meeting her in person for the first time, Hardison calls her "one sexy librarian"). Or at least, she would fit the trope, if she were a real person, rather than a part played by a grifter auditioning for the team. She passed.
A more straight example is Maggie, Nate's ex-wife. She is an art expert, which is how she and Nate met.
Kelso on That '70s Show ended up impregnating a beautiful librarian, played by Shannon Elizabeth.
Lilith Sternin on Cheers and Frasier. She's actually The Shrink, but fits this trope by appearance and personality.
On the Britney/Brittany episode of Glee, Britney Spears adopts this look when she's playing the teacher in the Rachel's dream sequence (to the song "Baby One More Time" of course). Rachel, for her part, adopts the Catholic School Girls Rule outfit for the song, in imitation of Britney in the original video.
In a later episode, an It's a Wonderful Plot dream sequence where New Directions never formed, Rachel was working as a library page after graduation, and her appearance elicited this reaction from certain fans.
On a Community Valentines Day episode, Troy and Abed both fall for a sexy librarian. Being good friends, they agree to let her decide between the two of them at the holiday dance.
Troy: Why does being a librarian make her even hotter?
Abed: They're keepers of knowledge. She holds the answers to all our questions, like 'Will you marry me?' and 'Why are there still libraries?'
Troy: I wanna be a book. She could pick me up...flip through my pages...make sure no one drew wieners in me...
On Parks and Recreation, Tammy II—Ron Swanson's second ex-wife—is (being played by MeganMullally) one of these. Combined with Scary Librarian. Also a sex fiend. Who turns Ron into one when she gets together with him. This is a major reason the Parks Department hates the Library.
Lisa Loeb has the look.
The music video for Tears For Fears' song Head Over Heels features a Hot Librarian.
The journalist in the music video for Adam Ant's "Goody Two Shoes." Complete with the glasses-off, hair-down, top-button bit at the end.
In fact, Adam Ant seems to do this rather a lot. While not strictly this trope, "Strip" music video has a very prim, proper woman in glasses shown throughout the clip, until the end, when she flips out, kicks over a table and, you guessed it, takes off the glasses and starts to strip
The Beatles' "Lovely Rita" has the characteristics of a hot librarian.
My Morning Jacket has a song off of Evil Urges called "Librarian", which includes the lyrics "Simple little bookworm,/Buried underneath/Is the sexiest librarian./Take off those glasses and let down your hair for me." It's a really good song, too.
The music video for Ludacris' "Splash Waterfalls" features one, getting turned on Ludacris through webcam.
Bret from Blue Stahli has jokingly claimed this is his fashion style.
Myth and Legend
The modern Hot Librarian is anticipated in spirit by Athena from Classical Mythology: virgin, warrior, goddess of wisdom, protector of civilization. Also, quite hot, and desired — but never actually achieved -— by any man, god, titan, or other being. Older Than Feudalism.
The iconic Twilight Caste Solar, Arianna, was a librarian (well, maid working at a library) who exalted while reading poetry (actually a cipher from the First Age). Technically only average in appearance, but tell that to the artists.
The iconic Casteless Lunar, Madame Vert, who plays the part of a grieving widow taking care of her dear departed husband's library for his friends during the day... And seducing the local prince under the light of the full moon, in her beastman (beastwoman?) form no less.
The Elder No Moon Lunar, Raksi, has taken the ruins of Sperimin, the greatest centre of learning in the First Age, and renamed them Mahalanka - the City of Ten Thousand Golden Delights. While she is actually some fifteen hundred years old, she also hasn't aged a day since she was 16.
There's also Cynis Megara, an Air Aspect Terrestrial who feels like an outcast (note; not Outcaste) due to her scholarly inclination and talent for Sorcery - as opposed to the rest of her family, being decadent nobles to the core.
The archetypal (and possibly first) Hot Librarian was Marian Paroo from the play and film The Music Man, who was literally the town librarian.
What can I do my dear/ to make it clear/ I love you madly, madly madame librarian, Marion!
The title character of the game Bayonetta, to the point that people joke about her resemblance to Sarah Palin.
Quistis Trepe of Final Fantasy VIII certainly applies for the hot part, if not the librarian. She became a teacher at the age of 18 because she was a prodigy, though she did get fired after a year for not having "good leadership skills" (Seifer was one of her students, and look how that turned out). Even that gets reversed by the end, so it's all good.
Victorian Principles, from Leisure Suit Larry 7, a literal librarian example. One of Larry's goals, which he eventually achieves all too well, is to unleash her inner sex maniac, which he accomplishes by swapping one of her books with The Erotic Adventures of Hercules.
Jolene from Paper Mario: The Thousand-Year Door. On the job, she wears average business attire and glasses, but in the local juice shop, she sports a cocktail dress and loses the glasses. She doesn't actually say her name, just the fact that you already know her rather well.
TeeTee in Monster Rancher 4, Ms. Fanservice when you meet her, ends up working for a scholarly type of guy at one point and tries to pull off this trope by adding the librarian with the clothes and letting her own looks supply the "hot".
The Professor from Contact reacts to Terry's apparent crush on Nadia by saying she has a sort of "Evil Librarian" vibe to her.
Yuuko from Katawa Shoujo is one of these when she's not working at the café.
This is one of the two most common interpretations of Koakuma from Touhou, as an orderly and shy aide of Patchouli. The other interpretation is less prude. Either version is dressed properly, though.
Patchouli herself is often depicted as attractive in the fanart, too. Whether this is intentional or not is anyone's guess is anyone's guess due to ZUN's signature art.
The Matrix Path Of Neo has an unnamed hot librarian potiental. She has the glasses, wears a tight, brown skirt-suit and has her hair up in a bun.
In Groovy Kinda, Anya Langerak appears to be a shy, somewhat overweight Cute Bookworm. As the story unfolds, we find out that this Children's Librarian is the former love slave to Eleanor, and has a deep submissive streak. She also sports some world-class cleavage when hosting a dinner for Larry and Edison.
Phix in Wapsi Square is the curator of the Bibliothiki, a library in some nearby dimension that apparently houses every book ever written. Oh, and she's not only a hot babe but also a sphinx. Recently she was seen in (very tall) human form dating Monica's boss at the museum.
Clarice of Girls with Slingshots fame wants to be a librarian, but for now is settling as a porn shop clerk and part-time dominatrix. She eventually became a part-time dominatrix/librarian, and even later gave up the dominatrix work because she was attracting stalkers in the library.
One of the antagonists of Goodwill Heroes is named The Sexy Librarian, just in case the subtlety of her ensemble was lost on you.
Dubious Company's Tiren has this look in the highschool arc. Hilariously, all the artist did was put her in a suit instead of her ninja garb.
In Rhapsodies Bookstore owner, Kate, tries to make sure no one find out how good she looks with her hair down and wearing anything besides her usual thriftstore ensemble.
Marina Orlova, a.k.a. Hot for Words, built herself on this trope. A beautiful young Russian philologist, she publishes weekly YouTube videos defining and exploring the etymologies of requested words and phrases... all the while reminding her viewers that intelligence is really sexy.
Silvia Marpole from An Extremely Goofy Movie is just like this, seeming to have never got over the end of the 70's and turned to books to compensate. Later in the film, Goofy, who never really noticed the decade was over, manages to convince her into a Beautiful All Along moment (with bell bottoms and boobtubes, no less!)
The Simpsons has an episode in which Marge and Lisa go to see the movie Tango de la Muerte, in which an aspiring champion dancer rejects all other partners to prefer a librarian "who's only read books on dancing". The dancer then takes her in his arms and spins her around a couple of times, prompting her glasses to fall off, her hair to come undone, and the top button of her blouse to pop off, precisely in that order.
Lisa has a crush on an older boy who works in the library, even though he's a jerkass.