On the Greek island of Kalokairi, 20-year-old bride-to-be Sophie Sheridan(Amanda Seyfried) posts three wedding invitations("I Have a Dream") to three different men. From across the globe, they set off for the wedding.
Sophie’s two bridesmaids arrive and she reveals that she found her mother’s diary and learned she has three possible dads: New York-based Irish architect Sam Carmichael(Pierce Brosnan), Swedish adventurer and writer Bill Andersson(Stellan Skarsgård), and British banker Harry Bright(Colin Firth). She invited them without telling her mother, believing that after she spends time with them she will know who her father is("Honey, Honey").
Villa owner Donna Sheridan(Meryl Streep) is ecstatic to reunite with old friends and former Donna and The Dynamos bandmates, wisecracking author Rosie(Julie Walters) and wealthy multiple divorcee Tanya(Christine Baranski), and reveals her bafflement at her daughter’s desire to get married. Donna explains her precarious finances to Rosie and Tanya("Money, Money, Money").
The three men arrive, and Sophie smuggles them to their room and explains that she, not her mother, sent the invitations. She begs them to hide so Donna will have a surprise at the wedding: seeing the old friends of whom she "so often" favorably speaks. They overhear Donna working(humming "Fernando") and swear to Sophie they won’t reveal her secret.
Donna spies them and is dumbfounded to find herself facing three former lovers she could never forget("Mamma Mia"), and is adamant that they leave. She confides in Tanya and Rosie("Chiquitita") a secret she has kept from everyone — she is uncertain which of the three men is Sophie’s father. Tanya and Rosie rally her spirits by getting Donna to dance with the female staff and islanders("Dancing Queen").
Sophie finds the men aboard Bill’s yacht, and they sail around Kalokairi("Our Last Summer") and tell stories of Donna as a carefree girl. Sophie musters up the courage to speak with her fiancé Sky(Dominic Cooper) about her ploy, but loses her nerve. Sky and Sophie sing to each other("Lay All Your Love on Me"), but are interrupted when Sky is kidnapped for his bachelor party.
At Sophie’s bachelorette party, Donna, Tanya, and Rosie perform as Donna and The Dynamos("Super Trouper"). Sophie is delighted to see her mother rock out, but becomes nervous when the festivities are interrupted by the arrival of Sam, Bill and Harry. She decides to get each of her three prospective dads alone to talk.
While her girlfriends dance with the men("Gimme! Gimme! Gimme!(A Man After Midnight)"), Sophie learns from Bill that Donna received the money to invest in her villa from his great aunt Sofia. Sophie guesses she must be her namesake and Bill is her father. She asks him to give her away and to keep their secret from Donna until the wedding.
Sophie’s happiness is short-lived as Sam and Harry each tell her they must be her dad and will give her away("Voulez-Vous"). A shocked Sophie can’t tell them the truth and, overwhelmed by the consequences of her actions, faints.
In the morning, Rosie and Tanya reassure Donna they will take care of the men. On Bill’s boat, Bill and Harry are about to confide in each other, but are interrupted by Rosie.
Donna confronts Sophie in the courtyard, believing Sophie wants the wedding stopped. Sophie says that all she wants is to avoid her mother’s mistakes and storms off. An upset Donna is accosted by Sam, concerned about Sophie getting married so young. Donna confronts him and both realize they still have feelings for each other("SOS").
Down on the beach, Tanya and young Pepper(Philip Michael) continue their flirtations from the previous night("Does Your Mother Know").
Sophie comes clean to Sky and asks for his help. He reacts angrily to his fiancée’s deception and Sophie turns to her mother for support. As Donna helps her daughter dress for the wedding, their rift is healed and Donna reminisces about Sophie’s childhood and how quickly she’s grown("Slipping Through My Fingers"). Sophie asks Donna to give her away. As the bridal party walks to the chapel, Sam intercepts Donna and begs her to talk. She reveals the pain she felt over losing him("The Winner Takes It All").
During the wedding, Donna tells Sophie that her father is present but he could be any of the three candidates, whom Sophie admits to inviting. For the rest please see this movie and enjoy the ending.