Writer/director Noah Baumbach seems to enjoy exploring the dark underbelly of family dynamics and relationships. Baumbach wrote the 2005 film The Squid and the Whale, in which the father (Jeff Daniels) of an intellectual, if slightly eccentric, Brooklyn family claims to have been a great novelist but has settled into a teaching job.

When his wife (Laura Linney) unveils a writing talent of her own, jealousy tears the family apart. The couple's two teenage sons are forced to rebuild their relationships with their parents. They must deal with a myriad of feelings when mom begins dating the younger son's tennis coach and their father has an affair with the girl his older son has been pursuing.

Margot at the Wedding finds Baumbach once again exploring the darkest aspects of family relationships. Margot (Nicole Kidman) is a Manhattan-based writer who is traveling to the coast with the oldest of her two boys, Claude (Zane Pais in his film debut) to attend the wedding of her sister Pauline (Jennifer Jason Leigh). Margot had originally declined the invitation to protest what she feels is a bad decision on Pauline's part. The younger sister has only known her fiancé Malcolm (Jack Black) for less than a year and Margot's decision is resolute.

From the moment Margot arrives at the family home, the tension between the sisters is palpable. Margot is further dismayed by Malcolm's unattractiveness and his unemployed status. That night, Margot tells her husband Jim (John Turturro) all about Malcolm's various shortcomings. Despite Margot's judgmental nature, her own marriage is far from perfect. She asked her husband not to travel with her to the wedding because he is completely unaware that Margot intends to leave him.

As it turns out, Margot has been having an affair with Pauline's neighbor and fellow writer Dick Koosman (Ciaran Hinds), who can only be described as a total loser. Pauline discovers the affair, disapproves of the whole thing, and is offended by Margot's motivation for the visit. While the two sisters claim to be each other's closest friends, they look for any opportunity to ridicule each other. Their animosity runs so deep; neither sister hesitates to drag their children Claude and Ingrid (Flora Cross) into their deeply troubled relationship. Claude doesn't realize his mother is planning to leave his father and Ingrid is unaware that her mother is pregnant with Malcolm's child.