The movie is based on the young adult book, The Sisterhood of the Traveling Pants, by Anne Brashares. As four best friends spend their first summer apart from one another, they share a magical pair of jeans. Despite being of various shapes and sizes, each one of them fits perfectly into the pants. To keep in touch they pass these pants to each other as well as the adventures they are going through while apart.
For the first time since their friendship began, the girls will be separated for a summer. Lena visits her grandparents in Greece and meets Kostos. Tibby remains at home, films a movie, and befriends a young girl named Bailey. Bridget goes to soccer camp in Mexico and falls in love with Eric, one of the coaches at the camp. Carmen visits her dad in South Carolina and finds out a shocking secret.
Tibby Tomko-Rollins, Lena Kaligaris, Carmen Lowell and Bridget Vreeland have been best friends since childhood. In the beginning of their summer vacations, they find a pair of jeans that fits each one of them perfectly; they decide to share the pants as a magic symbol of their friendship and form a sisterhood with a manifesto of ten rules. Bridget travels to a soccer camp in Mexico and she has a crush on the coach Eric, who is older than her. Lena visits her family in Greece and has a crush on the local fisherman Kostas and finds that there is a feud between their families. Carmen travels to South Caroline to spend the vacation with her father and she finds that he will marry the divorced Lydia Rodman. Tibby stays in town working in a department store to raise money to buy new equipment for her documentary and is befriended by the twelve year old Bailey that is very ill. After their vacations, they grow-up and their friendship remains solid as never.
Four best girlfriends hatch a plan to stay connected with one another as their lives start off in different directions: they pass around a pair of secondhand jeans that fits each of their bodies perfectly.
- The movie follows four teenage girls during a summer in which each goes through a crucial life experience. They succeed due to their loyal support of each other, symbolized by a pair of jeans (the "Travelling Pants") that they take turns wearing.
Shy Lena visits European relatives on an picturesque Greek island. She falls in love with a sensitive boy in spite of the fact that their families are having an old-fashioned feud. She learns to assert herself and finally wins the family's permission for a final meeting with her lover.
Brash Bridget, an athlete, goes to sports camp and is attracted to one of the coaches. He returns her love but is more concerned with keeping his job, which he will lose if they are caught. Bridget pursues him anyway and persuades him to make love to her on a beach. He panics and breaks off the relationship, and she realizes that she has thrown away her virginity for nothing (The sexual contact is off-screen and implied, rather than stated as a fact.).
Tibby, a sour-tempered girl, decides to make a "suckumentary" with her video tools, expressing her view of the world. During the summer she befriends Bailey, a girl who turns out to be dying from leukemia. After Bailey's death, Tibby is as bitter at life as ever, but discovers that Bailey left behind a video message, thanking Tibby for her friendship and urging her not to let Bailey's tragedy blight her life.
Carmen, an emotional girl with low self-esteem, visits her estranged father and discovers that he is marrying a divorcee with teenagers of her own. Although they are blandly polite, Carmen feels like an outsider and suspects that they resent her "intrusion", and so she finally turns home. The Sisterhood urge her to attend the wedding anyway, loaning her the "magic" jeans and coming along for moral support. Her father spots her in the audience and invites her to stand with him at the altar as he marries, and she feels accepted after all.