The thoughtful friend, whose first-person narratives open and close the novel. Carmen is the most introspective of the four girls, and she recognizes the importance of their friendship more clearly than the other girls do. Half Puerto Rican and half white, Carmen lives with her mother, Christina. Her plans for spending a summer with her father, Albert, in South Carolina are ruined when she discovers that Albert is engaged to a woman with two teenage children, all of them blond.
The rebellious, sarcastic friend who learns valuable life lessons thanks to her young friend, Bailey. Tibby is the only friend who stays home in Bethesda, Maryland, for the summer, and she has a healthy dose of scorn ready for all the people from her hometown, whom she sees as ridiculous losers. She spends her time working at Wallman’s and working on her documentary with Bailey. Tibby eventually learns to look beyond people’s exteriors and see what’s inside.
The athletic, daring friend who spends the summer at soccer camp in Baja California, Mexico. Bridget is impulsive, courageous, and a little reckless, but her extroversion and high spirits help her to make friends easily. She’s an ace soccer player, but she can sometimes be too aggressive, and she is often scolded for not being a team player. Bridget falls in love with a coach named Eric, an experience that leaves her devastated. Bridget’s mother died (probably a suicide) many years ago.
The shy, beautiful friend who travels to Oia, Greece, to spend the summer with her grandparents. Lena is introverted and quiet, happiest when she can spend time alone and paint. She distrusts all boys, certain they like her only for her looks, and she automatically writes off Kostos, the Greek boy her grandmother tries to set her up with. Her inability to open up to people leads her to make a confusing mess out of an unexpected encounter she has with Kostos. Fearing she’ll be alone forever, she eventually forces herself to tell Kostos she likes him.
Carmen’s mother, who works as a legal secretary. Though Carmen fights with her a lot, Christina is always there for her and helps Carmen to understand why she’s unwilling to get mad at her father.
Carmen’s father. Albert failed to tell Carmen he was engaged and that he’d moved to a new house, thinking it’d be best to tell her in person. However, his efforts to spare Carmen pain actually make things worse. He doesn’t know how to communicate effectively with Carmen, preferring instead to just pretend everything is okay.
Albert’s fiancée and Carmen’s soon-to-be stepmother. Lydia is obsessed with planning her wedding, because she didn’t have a real wedding the first time around. Her ex-husband is a recovering alcoholic. Lydia does her best to be kind to Carmen, but she struggles to truly connect with her.
Lydia’s sixteen-year-old daughter and Carmen’s soon-to-be stepsister. Krista struggles with geometry and eventually accepts Carmen’s help. She has no contact with her father.
Lydia’s eighteen-year-old son and Carmen’s soon-to-be stepbrother. Paul rarely speaks, but he proves to be a friend of sorts to Carmen. He visits his father, a recovering alcoholic, every month.
Paul’s mean, skinny girlfriend.
A twelve-year-old girl with leukemia. Bailey collapses in Wallman’s one day, and Tibby rides in the ambulance with her to the hospital. Feisty, persistent, and wise beyond her years, Bailey befriends Tibby and helps her lose some of her biting, sarcastic ways. Bailey, who was diagnosed with cancer when she was seven years old, dies at the end of the novel.
Bailey’s mother. Mrs. Graffman is grateful to Tibby for making Bailey’s summer so much fun.
Tibby’s young brother and sister.
The housekeeper and babysitter for Tibby’s siblings.
Tibby’s boss at Wallman’s. Duncan is a stickler for the rules of the workplace.
A Wallman’s employee with super-long fingernails. Angela and Bailey become friends without Tibby’s realizing it, and Tibby feels bad for judging Angela and for not seeing beyond her nails.
A ticket taker at the movie theater who can recite movie dialogue by heart. Margaret seems to Tibby like someone worthy of ridicule, but she’s actually very lonely.
A video game lover who’s obsessed with Dragon Master. Brian is the first person Tibby interviews for her film. Although she had written him off as a loser, she eventually befriends him and realizes he may have a lot to teach her about happiness.
A teenager in Tibby’s hometown whom Tibby has a crush on. Tucker seems to be interested in Tibby, but Bailey shows Tibby that Tucker isn’t worth her time.
A Greek boy whom Lena’s grandmother selects as a perfect match for Lena. Kostos is handsome and kind, and he was raised in Greece after his parents and brother were killed in a car accident in the United States. When Kostos accidentally sees Lena skinny-dipping, Lena thinks he was spying on her, and she inadvertently suggests to her grandparents that Kostos attacked her. Kostos is in love with Lena, and they kiss before she leaves Greece.
Lena’s fourteen-year-old sister. Effie is charming and talkative, often relieving the awkwardness that comes from Lena’s shyness. She is a shameless flirt and dates a waiter named Andreas in Greece.
Lena’s grandmother. A warm, loving woman and an excellent cook, Grandma wants nothing more than for Lena to fall in love with Kostos.
Lena’s grandfather. A quiet man who doesn’t speak English, Grandpa is actually more like Lena than any other member of the family. He and Lena bond during their silent breakfasts.
A coach at Bridget’s soccer camp. Bridget develops an intense crush on Eric even though coach/camper relationships are forbidden. He falls for her too but regrets it when he and Bridget become intimate. He can’t get over their age difference and feels guilty for giving in to his feelings.
Bridget’s team coach at soccer camp. Molly recognizes Bridget’s talent but often chastises her for not being a team player.
Bridget’s friends at soccer camp.