Fotoula "Toula" Portokalos (Nia Vardalos) is going through an early midlife crisis. At thirty, having had her childhood, adolescence and adult life plagued by bad luck, she feels that she is the only woman in her family who has "failed" at being a typical Greek girl. Her family expects her to be more like her 33-year-old sister Athena (Stavroula Logothettis) and marry a Greek boy, make Greek babies, and "feed everyone until the day she dies." Instead, Toula is stuck working in the family restaurant in Chicago, "Dancing Zorba's." Frumpy and cynical, she fears that she is doomed to be stuck with her life as it is and always has been. One day while at the restaurant, Toula briefly becomes enamored with and embarrasses herself in front of Ian Miller (John Corbett), a handsome school teacher.
Maggie Carpenter (Julia Roberts) is a spirited and attractive young woman who has had a number of unsuccessful relationships. Maggie, nervous of being married, has left a trail of fiancés. She's left three men waiting for her at the altar on their wedding day (all of which are caught on tape), receiving tabloid fame and the dubious nickname "The Runaway Bride".
Julianne Potter (Julia Roberts), a 27-year-old New York restaurant critic, receives a call from her longtime friend Michael O'Neal (Dermot Mulroney). In college, the two made an agreement that if neither of them were married by the time they turned 28, they would marry each other. Three weeks before her 28th birthday, Michael tells her that in four days, he will marry Kimmy Wallace (Cameron Diaz), a 20-year-old University of Chicago student from a wealthy family.
Annie Walker (Kristen Wiig) is a single woman in her late 30s. Following the failure of her bakery, she lost her boyfriend and her savings, forcing her to take a job as a sales clerk in a jewelry store and to share an apartment with an obnoxious roommate Gil (Matt Lucas) and his sister Brynn (Rebel Wilson). Her business's failure was so painful that she has given up baking entirely. She has a no-strings-attached sexual relationship with the self-absorbed Ted (Jon Hamm) but hopes for something more from him. Her best friend, Lillian (Maya Rudolph), is virtually her only source of happiness.
John Beckwith (Owen Wilson) and Jeremy Grey (Vince Vaughn) are divorce mediators in Washington D.C. The two friends frequently "crash" wedding parties to meet and bed women, working from a set of rules taught to them by a retired crasher, Chazz Reinhold.
The film follows the adventures of a group of friends through the eyes of Charles (Hugh Grant), a good-natured but socially awkward Briton, who is smitten with Carrie (Andie MacDowell), an American whom Charles repeatedly meets at four weddings and at a funeral.
On the occasion of his daughter Connie's wedding, Vito Corleone hears requests in his role as the Godfather, the Don of a New York crime family. Vito's youngest son, Michael, wearing a Marine Corps uniform, introduces his girlfriend, Kay Adams, to his family at the reception. Johnny Fontane, a famous singer and godson to Vito, seeks his help in securing a movie role; Vito dispatches his consigliere, Tom Hagen, to Los Angeles to talk the abrasive studio head, Jack Woltz, into giving Johnny the part. Woltz is unmoved until he wakes up in bed with the severed head of his prized stallion.
The film begins with a voiceover from David (Hugh Grant) commenting that whenever he gets gloomy with the state of the world he thinks about the arrivals terminal at Heathrow Airport, and the pure uncomplicated love felt as friends and families welcome their arriving loved ones. David's voiceover also relates that all the messages left by the people who died on the 9/11 planes were messages of love and not hate. The film then tells the 'love stories' of many people:
While on a date in a fancy restaurant with Michelle Flaherty, Jim Levenstein is ready to ask her to marry him. However, his dad still has to arrive with a ring because he forgot it. He tries to stall the question, causing her to think that he actually wants oral sex. She goes under the table and gives Jim fellatio just as Jim's dad arrives with the ring, causing her to bump her head on the table and attract the attention of the entire restaurant. Still, Michelle accepts the proposal.
Jane (Meryl Streep), who owns a successful bakery in Santa Barbara, California, and Jake Adler (Alec Baldwin), a successful attorney, divorced ten years earlier. They had three children together, two girls and a boy, who are grown. Jake, who was cheating on Jane, married the much younger Agness (Lake Bell).
Chuck Levine, a womanizing bachelor, and Larry Valentine, a widower struggling to raise his two children, are two veteran New York City fire fighters. During a routine sweep of a burned building, a segment of floor collapses on Chuck. However, Larry quickly shields him from the falling debris, saving his life. Later, he and Chuck wake up in a hospital, where Chuck vows to repay Larry in any way possible. This incident serves as a catalyst for Larry's epiphany: death is both inevitable and unpredictable. This prompts him to significantly increase his life insurance policy, but he runs into difficulties naming his children as primary beneficiaries in his policy. He is told he should get remarried so his new spouse could be the primary beneficiary; however, it doesn't specify who he has to marry. Inspired by a newspaper article about domestic partnerships, Larry asks Chuck to enter a civil union with him. Although Chuck declines at first, he is reminded of his debt to Larry and finally agrees, entering a domestic partnership and becoming Larry's primary beneficiary in the event of his death. To their dismay, however, New York City investigators soon arrive to inquire about their abrupt partnership, under suspicion of fraud. Chuck and Larry decide to enlist the help of lawyer Alex McDonough, played by Jessica Biel, who suggests they get married and move in together to prove they're committed. Chuck reluctantly agrees. The pair soon travel to Canada for a quick marriage (so quick they use a nearby homeless person as the best man) and begin living together.
Claude Verneuil, a Gaullist notary, and his wife Marie, a Catholic bourgeois from Chinon, are parents of four daughters: Isabelle, Odile, Ségolène, and Laure. The three eldest are already married to men, each one of a different religion and a different 'ethnic' origin: Isabelle married Rashid Ben Assem, a Muslim Arab, Odile married David Benichou, a Sephardi Jew, and Ségolène married Chao Ling, a Chinese man. The Verneuils pretend to accept their sons-in-laws but have had a hard time hiding their comfortability in accepting people into the family from outside the community. A family meeting is spoiled because of the awkwardness and clichés about race and religion, stated as much by the father as by the sons-in-laws who even exchange insulting communitarist views to and about each other.
Jane Nichols (Katherine Heigl) has been a bridesmaid for twenty-seven weddings. One night when she is attending two weddings almost simultaneously, she meets Kevin Doyle (James Marsden), who helps her home but disgusts her with his cynical views of marriage. He finds her day planner which she'd forgotten in the cab they shared. Meanwhile, Jane's sister Tess (Malin Åkerman) falls in love with Jane's boss George (Edward Burns) at first sight. Tess pretends to like the same things that George does so that she can get him to like her. Despite loving George herself, Jane does not reveal the truth and her sister's courtship progresses rapidly. Soon the new couple announces that they intend to marry in only three weeks and Jane becomes the wedding planner.
Charlotte "Charlie" Cantilini (Jennifer Lopez) is a temp/dog walker/yoga instructor and aspiring fashion designer from Venice Beach, California, who meets surgeon Kevin Fields (Michael Vartan). She thinks he's gay at first, based on a lie Fiona (Kevin's ex-girlfriend) told her. But then Kevin asks her out, and Charlie believes that she's finally found the right man.
In 1985, Robbie Hart (Adam Sandler) is an engaging and entertaining wedding singer from Ridgefield, Washington. He is engaged to his long-time girlfriend, Linda (Angela Featherstone), who was attracted to him at a time when he dreamed of becoming a rock star. Robbie meets and befriends a waitress, Julia Sullivan (Drew Barrymore), at the reception hall where he regularly performs. Julia is also engaged, to businessman Glenn Gulia (Matthew Glave) and he promises to sing at their wedding.