The Sisterhood of the Traveling Pants is based on the novel of the same name by Ann Brashares.
The movie centers around four teenage girls--Lena Kaligaris, Tabitha 'Tibby' Tomko-Rollins, Bridget Vreeland, and Carmen Lowell--who are best friends and have been together all their lives, but are about to separate for the summer. Lena is spending the summer in Greece with her grandparents; Tibby is staying at home; Bridget is going to soccer camp; and Carmen is visiting her father in South Carolina. On the eve of their separation, the girls visit a thrift shop and find a pair of pants that magically fits all four of them perfectly. The girls decide to share the pants among them equally over the summer as a way of keeping together when they are apart.