THEN: Lindsay Lohan played Cady Heron, a high school student who is forced to navigate manipulative friendships, dating, and gossip after moving to a new school.
NOW: 27-year-old Lohan is making a comeback after several stints in rehab and legal troubles.
The former child star, known for her leading roles in "Parent Trap" and "Life-Size," announced at the Sundance Film Festival this week that she will produce and star in a new film titled "Inconceivable."
The announcement follows Lohan's continued comeback from five years of rehab stints and run-ins with the law.
She's filming a docu-series for the Oprah Winfrey Network after a failed turn in the 2013 erotic thriller "The Canyons."
Since "Mean Girls," Lohan has also appeared on "That '70s Show" and "Ugly Betty" and has even released two music albums between 2004 and 2005.
NOW: McAdams, a bona fide movie star, plays a human rights lawyer in this month's post-9/11 thriller "A Most Wanted Man."
A decade after she ruled the school in "Mean Girls," McAdams has taken on a range of film roles, including her latest gig as a lawyer in "A Most Wanted Man" alongside Robin Wright and Philip Seymour Hoffman.
In 2004, several months after "Mean Girls" hit the big screen, McAdams played Allie in Nicholas Spark's romance novel-turned-film, "The Notebook." It was a role Roger Ebert noted for its "beauty and clarity."
McAdams has appeared in "Sherlock Holmes," "The Time Traveler's Wife," "The Vow," and "Midnight in Paris," just to name a few, and has picked up numerous MTV Movie Awards and Teen Choice awards along the way.
NOW: Chabert shifted gears back to TV and recently appeared on the cover of Maxim.
Aside from a line of smaller acting gigs in TV shows and movies, Chabert will appear in this year's film, "Telling of the Shoes."
The 31-year-old former "Party of Five" star appeared on a November 2013 cover of Maxim.
NOW: Seyfried ditched a string of G-rated roles to play an adult film star in the 2013 flick "Lovelace."
After tagging along with Regina's mean girl clan, Seyfried had lead parts in romantic comedies "Mamma Mia!" and "Letters to Juliet," as well as a starring role as Cosette in 2012's award-winning "Les Miserables."
The 29-year-old actress has several movies in the works including "A Million Ways to Die in the West," penned by Seth MacFarlane and featuring Liam Neeson and Charlize Theron.
Above photo is from: "Lovelace."
NOW: Caplan plays Virginia Johnson, a human sexuality researcher, in Showtime's acclaimed "Masters of Sex."
Caplan has appeared in some big name television shows, including "New Girl," "True Blood," and "The League."
She also starred in the 2008 thriller "Cloverfield."
Above photo is from: "Masters of Sex"
NOW: Bennett has had guests roles in several TV shows and starred in several forgettable films.
Bennett went on to star in a slew of forgettable films, but you may recognize his face from the 'Declare Yourself' ad campaign urging young people to vote in the 2008 presidential election.
Above photo is from 2012's "Divorce Invitation," in which Bennet starred alongside Jamie Lynn Sigler.
NOW: Franzese has since appeared in movies "War of the Worlds" and "I Spit On Your Grave."
Spreading his wings, the Brooklyn-born actor has also curated art shows throughout the years.
NOW: Surendra veered away from an acting career to pursue modeling and art.
He may have been a nerd at North Shore High in 2004, but ten years later and Surendra is looking pretty good — check out these modeling photos.
He's also an artist, working with ceramics, candles, and calligraphy.
THEN: Tina Fey not only played high school teacher Ms. Norbury — she also wrote the "Mean Girls" screenplay.
NOW: Fey has risen to fame as Hollywood's top funny lady—starring in "30 Rock," a string of films, and hosting the Golden Globes two years in a row.
Tina Fey went on to create NBC hit show "30 Rock" and her role as Liz Lemon even earned her two Golden Globe awards.
In 2010, Fey left "Saturday Night Live" to pursue a film career with flicks such as "Date Night" with Steve Carrell, "Admission," and "Baby Mama."
One role she became most beloved for? That of Golden Globes co-host alongside pal and frequent co-star, Amy Poehler.
NOW: Poehler just won her first Golden Globe for her role as Leslie Knope in "Parks and Recreation."
Poehler picked up an award for Best Actress in a TV Comedy for "Parks and Recreation" the same night she joined fellow "Mean Girls" co-star Tina Fey as host of the ceremony.
The two funny ladies have a long history of sharing the stage, as both started their careers on "Saturday Night Live."
Poehler even played a young Liz Lemon on Fey's "30 Rock" and the two both appeared in "Baby Mama" and "Anchorman 2: The Legend Continues."
Poehler also went on to start Smart Girls -- an online network for young women.
NOW: Meadows stuck to a career in television, with his most recent gigs being on "The Goldbergs" and "Suburgatory."
He has also appeared on "30 Rock," "Grown Ups 2," and even TV movie "Mean Girls 2."
NOW: In her most recent role, Gasteyer joined "Mean Girls" co-star Tim Meadows on ABC's "Suburgatory."
Like Poehler, Fey, and Meadows, Gasteyer also made a name for herself in a decade-long role on "Saturday Night Live."
She has since gone on to appear in indie films such as "Robot & Frank," "Fun Size," and "Peeples." She also stars as Judge Patrice Lessner on "The Good Wife."
Gasteyer also found her way to a live stage, appearing as Elphaba in Chicago's rendition of "Wicked."
Above photo is from: "Suburgatory"
THEN: Neil Flynn played Cady's dad, a zoologist who relocates his family to Illinois after 12 years in Africa.
NOW: Flynn has had roles in both film and TV, most notably as the janitor on "Scrubs" and Mike Heck on Emmy-nominated "The Middle."