For a themed party, several things are needed: dress code or costumes, fitting decor and props, fitting music and guests willing to dress up. And obviously, the theme.
Good old classics are Wild West parties; tropical Hawaiian parties for casual occasions or for summertime; there are Hollywood glamour parties or classic black-and-white parties for something more formal, or under-the-sea themed parties or wanderlust themed parties for avid adventurers and travellers. Young kids might want superhero parties and little girls usually appreciate princess or unicorn parties. Popular themes are favourite books, films and shows du jour (for example, Harry Potter or Game of Thrones and other fantasy often pop up in The New '10s). It's often done for movie nights where the hosts and guests wear matching costumes while watching their favourite movies or shows (often a season premiere or finale). In fictionland, it often serves as a tribute and Shout-Out to creators' favourite fiction, countries and their cultures or various historical periods.
Themed parties take more effort than regular parties, but as everyone is willing to go the extra mile, it's supposed that it'll also be more fun. And it's a big win for the hosts: their party will be way more exciting and more memorable than any other party. The hostess will be the society queen for a really long time. Alternatively, it's often the loving parents who are willing to make their kid's birthday party extra special, making their child one of the most popular kids around. Such a party is usually treated as a Serious Business by the hosts. The guests are likely to appreciate it, but it can be seen as an extra thing to worry about and in the end, the extra effort might not even be worth it. Usually it's a party for many people, but a more intimate version for couples or small families is also fairly common. It's usually done to show that the characters who throw such a party (or show up at one) are fun, fun-loving, playful and creative. Party poopers complain about those parties, refuse to wear a costume or they don't show up at all. If a regular party is going badly, a last-minute change to a themed party can be done as a saving throw.
Characters are supposed to wear Coordinated Clothes to show that they belong to one social group who attend the very same party. It's a Costume Party, I Swear! is a related prank trope: One character is lead to believe they're invited to a costume party with a theme, but in fact, it's a regular party and they end up humiliated.
An important note: All Halloween costume parties, holiday parties, bachelor/bachelorette parties, baby showers or even birthday parties are technically parties with a theme, however, this list collects examples that go a step above and have a specific motif chosen for the party.
- In Back to the Future, Marty's Mom's prom is the "Enchantment Under the Sea" dance, and is ocean-themed.
- Bridesmaids: Helen throws a lavish Parisian-themed bridal shower for Lillian. Paris and French-themed party was originally Annie's idea (because she and the bride are Childhood Friends and she knows her very well). Helen, Lillian's new BFF, originally turned it down and later takes the credit. Annie brings a heartfelt handmade gift but Helen upstages her, too, by giving Lilian a trip to Paris with herself.
- Never Been Kissed: The high school kids discuss the theme of their prom and it's a serious business. It's supposed to be "Millennium", but it turns out another high school does that, too. Teachers suggest "Under the Sea" or decade-themed "the '80s", but the kids boo to those ideas. Josie suggests "Meant for Each Other": Famous couples throughout history. The kids love it but then they mostly dress in whatever costumes they like (e.g. Disco Barbie, Malibu Barbie, or Evening Gown Barbie). Josie and her date go as Rosalind and Orlando from Shakespeare's As You Like It. The gym is decorated with pink and gold as colours of love.
- Bridget Jones: Bridget's parents' friends host a "Tarts and Vicars" party. Women are supposed to stylize themselves as prostitutes while men dress up as clergymen. Too bad they call the theme off at the last minute and some people show up in costumes, which is extremely awkward.
- In the Dirty Bertie book Worms!, Angela has a pink-themed birthday party and Bertie goes as a worm.
- Octavia, one of Katniss's make-up artist in The Hunger Games, complained to her about how badly went her feather-themed birthday party.
- In the short story "The Unbirthday Birthday", a boy's birthday is forgotten so they have a mud-themed party on the next day (with chocolate mud cake and playing in the mud.
- Anthony from Love Anthony used to have Barney & Friends-themed birthday parties, with a Barney-shaped cake, year after year, long after the other kids had all outgrown the show. Later, Beth's book club throws a party based on the book she writes about Anthony, with French toast sticks and a white pebble on each napkin.
- The Big Bang Theory:
- Discussed in "The Middle Earth Paradigm". Sheldon is baffled that Penny's first Halloween party that she hosts is a generic Halloween party and that is doesn't have a specific theme or any restriction. He suggests several possible themes, like science-fiction, fantasy, comic-books, anime, TV , film, D&D, manga, Greek Gods, Roman Gods, or Norse Gods.
- In "The Prom Equivalency" episode, Penny reveals she went to seven themed proms: four "Under the Sea", two "Enchanted Evenings", and one "Night to Remember" which she was too drunk to remember.
- Brooklyn Nine-Nine: Charles goes to a Jamaican-themed party which is actually his ex-wife's engagement party. It's called "Jamaican Me Marry You" because they travel to Jamaica frequently. He desperately tries to find a date. His crush Rosa Diaz agrees to go with him as a favour for a friend, and she even wears a matching dress. It's one of the first times she is not dressed in her signature black leather jacket.
- Community, "Critical Film Studies": The study group throws a themed surprise birthday party for Abed, a pop culture enthusiast. The theme is Pulp Fiction. All the main characters except Abed are dressed as characters from the film: Jeff is Vincent Vega, Shirley is Jules, Britta is Mia Wallace, Troy is Pumpkin, Annie is Honeybunny, Chang is Butch, and Pierce is The Gimp. They even got him Pulp Fiction-themed presents: the wallet that says Bad Motherfucker and Marcelus Wallace's briefcase. Jeff is supposed to bring Abed but he keeps delaying them.
- "The One with Phoebe's Dad": Monica and Rachel throw a Christmas party, but their heating gets broken and the apartment is way too hot. They call it a Tropical Christmas party.
Monica: Look, if worse comes to worse, it gets a little warm, we'll call it a theme party.
- "The One where Rachel Smokes": Monica and Phoebe agree to co-host a surprise birthday party for Rachel. Monica takes over everything but allows Phoebe to take care of cups and ice. So Phoebe turns it into a cups-and-ice party. Cups are used to serve drinks and some food, as banners, a chandelier, other decor and party hats. And she brought crushed ice, ice cubes, dry ice and her ice cones are a huge hit as well.
- "The One with Phoebe's Dad": Monica and Rachel throw a Christmas party, but their heating gets broken and the apartment is way too hot. They call it a Tropical Christmas party.
- Gilmore Girls:
- In "That Damned Donna Reed", Rory prepares a Donna Reed dinner party for her boyfriend Dean. She wears a 50's dress and make-up, and she makes a very traditional meal for them, acting like a typical housewife from the time period. She also picks music, borrowing is specifically from her friend Lane.
- In "Here Comes the Son", Jess assures his Disappeared Dad Jimmy he doesn't want or need a Teenage Mutant Ninja Turtles themed party.
Jess: Raise me? I'm eighteen! I'm raised. I can vote, I can be drafted. It's a little late to throw me a Teenage Mutant Ninja Turtle birthday party.
- Lorelai and Sookie start a catering business. One of the parties they organize is a Lord of the Rings party. Lorelai does make-up for the kids, and they have costumes and swords for them as well. Sookie is a Supreme Chef, but she doesn't realize what kind of food kids like.
- Logan takes Rory to a Life and Death Brigade (a Yale secret society) gathering. It's somewhere in the middle of the woods. The dress code is safari Adventurer Outfits from the turn of the century. In the morning, they all wear formal attire: tuxedos and ball gowns, still in tents in the wood.
- Rory goes to a Quentin Tarantino-themed party at Yale. She goes as Gogo from Kill Bill because she has a very similar skirt from her old high school uniform. Most people wear costumes from Kill Bill or Pulp Fiction. The music is from those two films as well.
- Rory throws a Marx brothers' movie viewing party for herself and her friend Marty at their Yale dorm. She gets tons of food, decoration and hats and wigs for them to wear.
- Lorelai throws an Asian-themed party for Rory because Rory's upset. She and her boyfriend have been planning a trip to Asia and it has been cancelled. Lorelai wants to cheer her up so she turns their house into an Asian wonderland.
- Logan takes Rory (who has been arrested for joyriding in a boat) to a Surprise Party where their friends are dressed in old-school Institutional Apparel with black and white horizontal stripes and pillbox hats. They sing "She's a jolly good felon" for her.
- Rory's throws a very successful USO slash World War II-themed social event for Daughters of American Revolution. The hired staff, musicians and Rory herself wear costumes (e.g. Rory rocks a United Service Organizations uniform, a styled 40's hairdo with locks and she has very bright red lipstick). The guests are upper-class Americans who wear normal formal clothes.
- Rory organizes a British "bon voyage" party when her boyfriend Logan goes to work in London and they're gonna have a long-distance relationship. She's dressed up and tries to talk with a British accent. Their apartment is decorated with Union Jack flags, London sights and souvenirs. Logan jokingly calls her Mary Poppins to which she retorts she was going for Gwyneth Paltrow in Shakespeare in Love. She's actually some sort of a 1960s British Mod girl.
- Luke throws a birthday party for his pre-teen daughter April. Everyone is super bored because he didn't think of activities for the girls. Lorelai saves the day by organizing a make-up party. She takes the girls shopping and then they are allowed to experiment with nail polishes, eye shadows or lipsticks.
- One episode has the characters throwing a "Halfoween" party, as they wanted to celebrate Halloween again despite the holiday being six months away. Everyone is in costume, and the room is decorated not only with Halloween-decor but also "Half"-decor.
- Downplayed in "iPity The Nevel". The gang throws a "karma party" after Nevel's public humiliation. For the sake of a pun, the food served is "just desserts".
- In Jane the Virgin, Lina's bachelorette party is a Agatha Christie or Clue-esque Murder Mystery-themed party, because her fiance is a fan of the genre.
- Jessie: In "Tempest in a Teacup", the kids try to help Jessie with her second date with Tony and throw her a re-do of her high-school prom, complete with an underwater theme, where the walls are blue, and decorated with fake fish and seaweed.
- Lost: Hurley's mom gives him a tropical-island themed birthday party after he is rescued from the Island. Hurley and his fellow Oceanic 815 "survivors" are bemused by her choice.
Sayid: Interesting choice of theme.
Hurley: Yeah, my mom... really doesn't get it, dude.
- M*A*S*H: In "Peace on Us" the 4077th throws an "Anti-Green" party after Hawkeye complains about the overabundance of the color green. Everything is red, from the streamers decorating the mess tent to the hair and clothing of the personnel. A visiting major even turns out to have naturally red hair, much to the surprised amusement of the attendees.
- Murdoch Mysteries: In one episode, the characters attend an Alice's Adventures in Wonderland-themed party, supposedly to honour the recently deceased Lewis Carroll. It's actually a plot to get some characters on the same spot to start a revenge and some costumes are worn to disguise identity. Detective Murdoch is dressed as the Mad Hatter and Dr. Julia Ogden is Alice. (They have the most prominent costumes for the party, despite the fact that they are not especially close to the hosts and Murdoch wasn't even supposed to attend.)
- Ned's Declassified School Survival Guide: The big dance at the end of season 1 had an "Around the World" theme; every area in the school was designed to look like a different part of the world.
- Schitt's Creek:
- Roland and Jocelyn have an annual Hawaiian-themed bash.
- Patrick hosts a Slumber Party themed housewarming where the guests wear pajamas and play games.
- Sex Education: Moordale Secondary school hosts a fairy-tale themed dance called "Happily Ever After".
- Victorious: Hollywood Arts puts on a dance with a cowboy and luau theme, which everyone calls a Cowau.
- You: For Beck's birthday, her friend talks Joe into throwing a party at his bookstore, where people dress up as their favorite literary characters and writers.
- In Zoey 101, the gang's planning a surprise birthday party for Chase in one episode and, at one point, are trying to decide on a theme for it—either a pajama party or a beach party. The boys want to do a beach party, since it would be a good excuse for all the female guests to wear bikinis—but when Zoey reveals that she's planning on bringing Chase's grandmother to the party (not only because Chase and his grandmother are very close but also because they share the same birthday), the gang ultimately decides on doing a pajama party.
- The Bizarre Adventures of Woodruff and the Schnibble: Near the end of the game, Woodruff attends a party hosted by Coh Cott, themed around eyes.
- Club Penguin (a Defunct Online Video Game) had a lot of parties with unique themes at least once per month. All the places on the island were decorated, players could purchase special items and play minigames related to the event. Some of the more recurring parties were the Puffle Parties, Medieval Parties, Music Jam Parties and Holiday Parties with a theme. In its final years, it featured a lot crossover-themed parties (mainly with Disney), such as Marvel, Teen Beach Movie or Descendants.
- Hitman: Blood Money's mission "A Dance with the Devil" is set during a "Heaven and Hell"-themed party in the Shark Club. The top floor has the "Heaven" party which is decorated to look like Fluffy Cloud Heaven with angel costumes, while the basement has the "Hell" party, decorated to look like Fire and Brimstone Hell and with the guests wearing devil masks.
- Pet Society is a Defunct Online Video Game. Its virtual pets were cared for by their owners and certain weekly events were themed parties, often retro, glamorous or based in current sporting events, fiction and myths. They had a Hollywood Glamour style party, a fairy-themed party for Midsummer, an Alice in Wonderland week, witch-themed or ghost-themed Halloween parties, science or space themed parties, a beach party, sport-themed Olympics or Wimbledon parties, or an Ancient Egypt party or an adventure archeology party in the style of Indiana Jones and many others. Some creative players could make their own theme party with various 'normal' stuff to buy, like flower-themed party or a strawberry party. The pets could decorate their rooms and gardens with specific themed items, they could dress in various theme costumes and buy event-specific food. One of the ways to play and gain points was to invite friends' pets: they would come to one room and party together.
- Homestar Runner:
- In "The Luau", Marzipan hosts a Luau, a party featuring tropical island decor, the roasting of a giant block of tofu on a spit (the vegetarian equivalent of roasting a pig) and Polynesian poetry accompanied by Marzipan on a Ukulele. The thing is considered boring by Strong Bad and some other characters.
- In the Strong Bad Email "senior prom", the prom is called "Entrapment All Up On the Moon", a parody of the Back to the Future dance name, and is space-themed in its decor, featuring alien and moon cutouts.
- In Arthur, King of Time and Space, Arthur's school has a prom with a "My Only Sunshine" theme, and Guenivere's has a prom with a "Fish Under The Sea" theme. This means that the venues are in the characters' color-coding (yellow and blue, respectively), and their phone screens are showing the other's color when they dance together.
- Manic Pixie Dream Wife: Simone the manic pixie wife throws an under-the-sea themed dinner party just for her and her husband. And their pet fish joins them, too. She decorated their house and food, and she wears a mermaid costume.
- Todd in the Shadows: When Todd was in college, he and his friends would throw "ironic" frat-themed parties where they wore khakis and polo shirts and listened to music they didn't like. Todd now realizes that by "ironic" they really meant "jealous".
- The Bob's Burgers episode "Bobby Driver" has Tina, Gene, and Louise attending a kid's extravagant The Great Gatsby themed birthday party. The birthday-boy is very uninterested in the party and the kids initially think he's a spoiled brat who doesn't appreciate his parents' hard work. They later find out the parents threw the party for themselves so they could post photos of it on social media and the boy just wanted a low-key pizza party the whole time.
- In the Charlie and Lola episode "This is Actually My Party", Charlie has a monster-themed birthday party where his friends dress as and act like monsters.
- King of the Hill: In "Strangeness on a Train", Peggy plans her birthday party on a train: a murder mystery theatre train ride combined with 70's disco theme. Hank is not sure it's such a great idea, especially the disco part, but agrees with it to make Peggy happy. Their friends show up in their disco outfits, as well as most of the actors (but those have also costumes for their roles in the play). The party goes terribly wrong in so many directions. For instance, the train toilet ends up clogged with an Andy Warhol wig and Elton John sunglasses.
- In Rocket Power's episode "Typhoid Sam", Tito is planning a luau party, but his friend, Raymundo, reminds him of various times he had done theme parties, like the times he had done a toga party and a disco party, both of which ended up failing. Tito asks Raymundo to stop before reminding of another party.
- SpongeBob SquarePants: In "Texas", Spongebob throws a surprise Texas-themed party at the Krusty Krab so that Sandy (who's feeling homesick) doesn't have to go back to her hometown. While the "party" seems half-assed at best (for example, Spongebob serves "pecan pies" made with cans of peas), Sandy is touched that her neighbors care about her and decides to stay in Bikini Bottom.
- One episode of Barbie: Life in the Dreamhouse sees Raquelle, Barbie's rival, inviting her and Token Black Friend Nikki to a themed party. Nikki suspects a trap, and is proven right when Raquelle deliberately lies about the theme—it's "formal dress," and Barbie and Nikki show up in casual clothing. Barbie is Crazy-Prepared, though, and reveals that said outfits can become beautiful ball gowns at a moment's notice. Raquelle repeatedly tries to change the theme to upstage them (she cycles through "pool party" and "enchanted mermaid"), but it turns out the outfits can change to match those themes, too.
- In the Little Bear episode "Party at Owl's House", Owl decides to throw Emily a "because" party since summer is almost over. Owl, Emily, Little Bear, Cat, Duck, and Hen bring in pretend food there to celebrate but in the end, Mother and Father Bear join in the fun with some chocolate cake and lemonade.
- The main reason that Wyatt Williams from 6teen doesn't like having birthday parties is because his family (or at least his parents) insist that they be themed parties—in "Birthday Boy" (in which Wyatt celebrates his birthday), Wyatt's family decided on a redneck/"trailer park" theme for his current birthday and Jen claims that at a previous birthday party for Wyatt, everything was colored brown.