The film's main plot focuses on the wedding ceremony of Jim Levenstein (Jason Biggs) and Michelle Flaherty (Alyson Hannigan), while its subplot centers on Steve Stifler (Seann William Scott), and his outrageous antics including his attempt to organize a bachelor party, teaching Jim to dance for the wedding, and competing with Finch (Eddie Kaye Thomas) to win the heart of Michelle's sister, Cadence (January Jones).

Like the previous two films, American Wedding received mixed reviews from critics, who were again divided on its humor but praised the cast's performances, especially Scott's.

[5] The franchise was later expanded into a series of direct-to-DVD standalone spin-offs, under the umbrella title American Pie Presents, that began with the release of Band Camp (2005).

In East Great Falls, Michigan, in a restaurant, Jim Levenstein hints to his girlfriend Michelle that he is about to propose, until his dad calls to inform him he left the ring at home.

Jim and Michelle exclude their acquaintance, the boorish and vulgar Steven Stifler, from the wedding plans, but he notices the celebration party while passing and insists on taking part, seeing an opportunity to have sex with the bridesmaids.

Stifler, Jim, and his friends Paul Finch and Kevin Myers, travel to Chicago to secure Michelle's dream wedding dress, and trace the designer to a gay bar.

After Cadence agrees to sleep with Stifler, he steals a bottle of champagne from the kitchen, inadvertently turning off the cold room and killing the wedding flowers within.

Feeling guilty, Stifler works through the night to convince the florist to put together new floral displays, and enlists the help of his high school football team players and Bear.

Seeing the new display, Michelle and Jim forgive Stifler, and Cadence reconciles with him, seeing he does genuinely care about his friends, and agrees to have sex with him in a supply closet before the wedding.

Unaware that Cadence was also delayed, Stifler enters the dark closet and has sex with someone, revealed to be Jim's grandmother, who was put there by ushers because of her unlikable personality.

[6] The film's soundtrack includes songs by Van Morrison, Blue October, The Working Title, Foo Fighters, Feeder, Avril Lavigne, American Hi-Fi, Sum 41, the All-American Rejects, Joseph Arthur, New Found Glory, and Hot Action Cop.

The song "Into the Mystic", played at the end of the film when Jim and Michelle take to the dance floor at the reception, begins as Van Morrison's recording, but midway through it changes to The Wallflowers' cover version due to licensing reasons.

[19] Despite being absent from Wedding, lead ensemble cast members Chris Klein, Mena Suvari, Tara Reid, Shannon Elizabeth, and Natasha Lyonne all signed on to return for the fourth installment.