Heron quickly befriends two outcasts (Lizzy Caplan and Daniel Franzese), with the trio forming a plan to exact revenge on Regina George (McAdams), the leader of an envied clique known as the Plastics.

After being homeschooled for her entire life and having spent the last twelve years in Africa, 16-year-old Cady Heron begins her first day at North Shore High School.

The next day, Janis and Damian explain the school's various cliques to her, warning her about the "Plastics", a trio of pretty and wealthy but mean girls consisting of the ruthless queen bee Regina George, the insecure gossiper Gretchen Wieners, and the sweet but dimwitted Karen Smith.

Over the following months, Cady, with Janis and Damian's help, manages to trick Gretchen into revealing her secrets, break up Regina's relationship with Aaron (and spend time with him by pretending to need math tutoring), and cause her to gain weight by giving her high-calorie snack bars under the pretense that they are diet food.

After violating the Plastics' dress code rules by wearing sweatpants, the only thing that fit her, Regina is kicked out of the group and Cady becomes the new "queen bee".

To earn extra credit, Cady joins the school Mathletes, moderated by Ms. Norbury and led by fellow student Kevin Gnapoor, at the state finals, answering the tiebreaker correctly to win the championship.

The Plastics disband by the time senior year begins, as a fully-recovered Regina joins the school's lacrosse team to channel her anger positively, Gretchen joins the "Cool Asian" clique and becomes their biggest follower and Karen becomes the school weather girl while Cady begins dating Aaron as well as continuing to hang out with Janis, who starts dating Kevin, and Damian.

While reflecting to herself on the relative social peace that has taken over North Shore High, Cady notices a trio of new "Junior Plastics" and wonders how long they will last, as she jokingly imagines them being hit by a school bus.

Julia Chantrey plays Amber D'Alessio and Jacky Chamberlain and Olympia Lukis appear as disabled students Giselle Sgro and Jessica Lopez.

Tina Fey read Rosalind Wiseman's Queen Bees and Wannabes and called Saturday Night Live producer Lorne Michaels to suggest it could be turned into a film.

Amanda Seyfried originally auditioned for Regina, and although Waters thought she was "fantastic", the producers instead suggested her for Karen due to her "spacey and daffy sense of humor".

It was released in a special collector's edition, in both its original 1.77:1 widescreen aspect ratio and a 1.33:1 fullscreen crop, including several deleted scenes, a blooper reel, three TV spots, the theatrical trailer, previews, and three featurettes.

[28][29] In its opening weekend, Mean Girls grossed $24.4 million from 3,159 screens[30] at 2,839 theaters in the United States, ranking number one at the box office and averaging $8,606 per venue.

[31] Mean Girls received largely positive reviews;[32] critics lauded Lohan's and McAdams's performances and labeled the film as Seyfried and Caplan's breakthrough roles.

The site's critical consensus states: "Elevated by a brilliant screenplay and outstanding ensemble cast, Mean Girls finds fresh, female-fronted humor in the high school experience.

"[37] Ann Hornaday of The Washington Post wrote that it "boasts a one-two-three punch in star Lindsay Lohan, screenwriter Tina Fey and director Mark Waters, and, indeed, it delivers a knockout".

[39][37] In April 2004, Mick LaSalle of the San Francisco Chronicle wrote, "as in The House of Yes and Freaky Friday, Waters keeps it wild but real", noting that "all the supporting performances go right to the edge of absurdity without crossing the line into random zaniness.

"[41] In 2006, Entertainment Weekly had also named it the 12th-best high school film of all time: "While Mean Girls is technically a comedy, its depiction of girl-on-girl cattiness stings incredibly true.

[45] In March 2021, Richard Brody of The New Yorker ranked Lohan's performance as the eleventh best of the 21st century up to that point, praising her "blend of charisma and awkwardness, innocence and guile" as well as "faux-casual earnestness" she used for dialogue.

[79] In June 2018, the official Twitter account of the Israeli Embassy in the U.S. made headlines when it responded to a tweet by Iranian leader Ali Khamenei, calling Israel "a malignant cancerous tumor", with an animated GIF of the "Why are you so obsessed with me?"

[82] Multiple scenes have been reenacted and parodied by various celebrities throughout the years following its release, including Ed Sheeran, Iggy Azalea, Amber Rose and Waka Flocka Flame during a 2014 skit for MTV.

[92] In June 2021, actress Aimee Lou Wood mentioned the scene where Cady broke her Spring Fling crown in pieces and shared it with girls around her.

[...] That relevance almost two decades later proves that Mean Girls is deserving of its classic status,"[115] and Slashfilm's Ethan Anderton writing that the "generation-defining high school movie" not only captures the teenage culture of the early 2000s perfectly, "but it's also hilariously clever for being adapted from a non-fiction parenting advice book [...] Mean Girls is great because it captures that cruel teen vibe perfectly, and it tries to deliver a nice wholesome message to fight it, which kids will laugh at, agree with, and then never do anything about.

"[116] In September 2020, the Pillsbury Company released a limited edition of Toaster Strudel featuring pink icing and Mean Girls packaging to pay homage to its movie-claimed inventor's daughter, Gretchen Wieners.

[118] In November 2023, Walmart unveiled its annual holiday campaign featuring much of the original cast, including Lohan, Seyfried, Chabert, Franzese, and Surendra, reprising their roles as adults and recreating the film's scenes with modern twists.

[132] The original cast featured Erika Henningsen as Cady, Taylor Louderman as Regina, Barrett Wilbert Weed as Janis, Grey Henson as Damian, Ashley Park as Gretchen, and Kate Rockwell as Karen.

Titled Mean Girls: Senior Year, it picks up after the events of the film and centers on the arrival of a new student, Megan Moretti, who wants to be the most popular kid at school.

[148][149] The film is directed by Melanie Mayron and stars Meaghan Martin, Jennifer Stone, Maiara Walsh, Nicole Gale Anderson, and Claire Holt, while Tim Meadows reprises his role as the principal Ron Duvall.

"[158][159] In April 2020, Lohan was once again asked about the sequel by David Spade and confessed she had been hanging on to the idea of coming back to doing movies with that project "for a really long time" but that it was out of her hands.

"[164] In an August 2020 interview on the podcast Unspooled, director Mark Waters discussed an idea for a sequel where the main characters from the original movie would now be young mothers serving together in a parent–teacher association, adding that its development is entirely up to Fey wanting to write a screenplay.