Carmen Lowell
- Played By: America Ferrera, Tiarra Santana (young)
A sensitive, caring and dramatic half-Puerto Rican with an explosive temper and colorful personality. She was the member who found the pants. She is the glue that keeps the other gals together.
- Affectionate Nickname: Her dad calls her Bun; her friends call her Carma.
- Four-Temperament Ensemble: Choleric
- Sibling Yin-Yang: Stepsibling, at least. Paul is The Stoic and it's hard to get more than a monosyllabic response from him, if any, and Krista is a quiet, polite Valley Girl.
- Spicy Latina: Carmen's hurt feelings and temper lead her to throw a rock through her father's dining room window and then run away.
- There Are No Coincidences: In the books Carmen states that she sees signs everywhere and in book and film both believed the Pants were brought to them by fate.
Lena Kaligaris
- Played By: Alexis Bledel, Alanna Dawn Ekkert (young)
A beautiful and artistic girl of Greek heritage. She has a younger sister named Effie. She is very shy and withdrawn, due to being judged on her appearance.
- Dating What Daddy Hates: Downplayed in the fourth book, as while Lena thinks that her father wouldn't approve of her relationship with Leo, she also admits that he'd probably be upset about any boyfriend she had, and she doesn't date Leo long enough to introduce him to her family in the first place.
- Foolish Sibling, Responsible Sibling: The Responsible to Effie's Foolish.
- Four-Temperament Ensemble: Phlegmatic.
- Immigrant Parents: Her parents both hail from Greece.
- Sibling Yin-Yang: With her younger sister Effie.
Tabitha "Tibby" Anastasia Rollins
- Played By: Amber Tamblyn, Victoria Tennant (young)
The rebellious daughter of two former radicals. She is extremely interested in filmmaking. She lives with her parents and much younger siblings, Katherine and Nicky. She is disdainful, arrogant, and views the world as cynical and depressing.
- Brutal Honesty: Tibby prides herself on this till she gets a taste of her own medicine from the younger, equally snarky little girl she meets, Bailey.
- Eerie Pale-Skinned Brunette: Although more punk than eerie.
- Emotionless Girl: Carmen calls her out on this in this movie: "And why are you giving me this hypocritical lecture about treating people decently when you're the one who walks around saying screw the world because that's easier than having to feel something?!"
- Four-Temperament Ensemble: Melancholic.
- Hippie Parents: Before they settled down and focused on their careers and new kids, Tibby was raised by these.
- Took a Level in Kindness: Her summer with Bailey teaches her this.
Bridget Vreeland
- Played By: Blake Lively, Ashley Hale (young)
The athletic soccer star of the group. Has a twin brother named Perry, mother died when she was eleven and her father is a Dutch immigrant.
- Determinator: Especially in the first book regarding Eric.
- Did They or Didn't They?: She and Eric did.
- Disappeared Dad: She lives with him, but he completely blocks his children out for most of the series, to the point that he barely notices when she stays over at her friends' houses.
- Four-Temperament Ensemble: Sanguine
- Heroic BSoD: The entire year between the first and second book serves as one for Bridget.
- The Lad-ette: Downplayed. Brigitte forgot to pack clothes that didn't make her look like a boy, is very into soccer, is competitive, grew up with in a mostly-male home for quite awhile, but has 4 best friends who are female, flirted "outrageously" with Eric at camp, and isn't above using her looks to attract men.
- Sibling Yin-Yang: With her twin brother Perry.
Christina
- Played By: Rachel Ticotin
Carmen's mother. She's divorced and raises Carmen as a single mother. In the second book, however, she starts a relationship with a man called David. They go on to get married and have a son.
- Spicy Latina: Averted. Unlike Carmen, she doesn't really have a temper and is very sweet.
David Breckham
Albert "Al" Lowell
- Played By: Bradley Whitford
Carmen's father. Despite his and Christina's divorce, he and Carmen remained quite close, until he springs his new marriage with Lydia on her.
- Disappeared Dad: Though he and Carmen do remain in contact, are even close.
- Parent with New Paramour: He is planning to marry Lydia Rodman when Carmen comes to stay during the first summer.
- Poor Communication Kills: Albert doesn't let Carmen know that Lydia exists, let alone that they're engaged to be married, until she's already at his home and committed to spending the summer with him. Carmen likely would have been upset about her dad getting remarried either way, but Albert withholding the information until a couple of months before the wedding doesn't earn him very many points.
- Visit by Divorced Dad: He visits Carmen a couple of times a year. Carmen's plotline in the first book comes from an inversion in which she goes to visit him for the summer instead.
Lydia Rodman-Lowell
- Played By: Nancy Travis
- Everyone Loves Blondes: Carmen holds some resentfulness towards her "blondeness".
- Posthumous Character: By Sisterhood Everlasting, she has passed away from cancer.
Paul Rodman
- Played By: Kyle Schmid
Carmen's stepbrother, a stoic, popular athlete who is the man of the house till Albert marries Lydia. Carmen and Paul become somewhat close and she often talks to him for advice.
- Lovable Jock: Is a talented, well-liked athlete.
Krista Rodman
- Played By: Emily Tennant
Carmen's stepsister, younger by a year or two, presented as a foil to Carment with her skinny frame, blonde hair, and quiet, polite demeanor. Later she tries to act and dress like Carmen.
- Dumb Blonde: Carmen initially sees her as one, especially as Krista is unskilled at geometry, which Carmen loves doing.
- Proper Lady: Up until later books, when Carmen inadvertently inspires her to go through a rebellious phase.
- Southern Belle
- Valley Girl: Uses a lot of this slang despite being a Southern Belle.
Effie Kaligaris
- Played By: Lucy Hale
Lena's younger sister.
- Brutal Honesty: Lena, who is somewhat brutally honest herself, does not always appreciate this, especially when it comes to Kostos.
- Foolish Sibling, Responsible Sibling: Foolish to Lena's Responsible.
- The Glorious War of Sisterly Rivalry: Averted- Lena and Effie are very different but have a very good relationship with each other.
- Sibling Yin-Yang: With Lena.
- Shipper on Deck: She likes Lena and Kostos together.
Valia Kaligaris
- Played By: Maria Konstandarou
Alice Rollins
- Played By: Sarah-Jane Redmond
Tibby's mother.
- Give Him a Normal Life: Why the Rollins' quit their hippie lifestyles and get stable jobs with the birth of Nicky.
- Hippie Parents: To Tibby before their youngest children.
Mr. Rollins (given name unknown)
- Played By: Harry L Seddon
Tibby's father.
- Give Him a Normal Life: Why the Rollins' quit their hippie lifestyles and get stable jobs with the birth of Nicky.
- Hippie Parents: To Tibby before their youngest children.
Nicky Rollins
- Played By: Cory Nichols
Tibby's younger brother.
- Annoying Younger Sibling: Tibby sees him as this in his toddler years.
Katherine Rollins
- Played By: Carly Rose Sonenclar
Tibby's younger sister.
- Cheerful Child: Especially in the third book.
Marlene "Marly" Vreeland
- Played By: Kendall Cross
Bridget's deceased mother.
- Driven to Suicide: Implied.
- Everyone Loves Blondes: Was very popular and even a beauty queen in her early years.
Franz Vreeland
- Played By: Ernie Lively
Bridget's father.
Perry Vreeland
Bridget's twin brother.- Sibling Yin-Yang: With Bridget.
Greta Randolph
- Played By: Blythe Danner
Bridget's grandmother.
- Adaptational Attractiveness: In the book, she is described as fat, frumpy, diabetic and wearing Walmart clothes. In the movie, she is portrayed by the svelte and sophisticated Blythe Danner.
- I Was Quite the Looker: Bridget discovers from old photos that she and her mother got their blonde hair and beauty from Greta.
- Outliving One's Offspring: Her daughter died in her thirties.
- Team Mom: For Bridget, even when her mother was still alive.
Bailey Graffman
- Played By: Jenna Boyd
Bailey is a 12-year-old girl who has leukaemia. She becomes a close friend of Tibby's over the course of the first book. Near the end of the first book, she dies.
- Bratty Half-Pint: Bailey likes to act this way to test people and is actually nice, though.
Brian McBrian
- Played By: Leonardo Nam
- Asian and Nerdy: In the movies.
- Dogged Nice Guy: He adores Tibby and is utterly loyal to her even when she's hurt him (he did give up once, but forgave her).
- Nerds Are Sexy: Tibby comes to think so, though it helps that she gets Brian to shower more regularly and dress better.
- Race Lift: Doesn't appear to be of Asian descent in the books as he is in the film.
Eric Richman
- Played By: Mike Vogel
Eric first appears in the first book as a soccer coach in the camp where Bridget spends her summer. She falls in love with him. However, near the end of the book he tells her that they can't be together because of their age difference. In the third book, two years after this, Bridget meets him again, and this time they end up becoming a couple.
- Amoral Attorney: Inverted. While his law school friends take jobs at fancy firms that pay twice as much as what he's making, he works a much more modest job as an immigration lawyer and only takes cases he believes in.
- But Not Too Foreign: In the books, it's stated multiple times that his mother is Mexican, and his heritage seems to mean a lot to him. But having an Anglophone surname – and being portrayed in the movies by Mike Vogel, who is white and of European descent – his heritage is easily tossed aside.
- Official Couple: After his return in the third book, he and Bridget are this.
