Babel focuses on four interrelated sets of situations and characters, and many events are revealed out of sequence. The following plot summary has been simplified and thus does not reflect the exact sequence of the events on screen.
Bob Harris, an aging American movie star, arrives in Tokyo to film an advertisement for Suntory whisky. Charlotte, a young college graduate, is left in her hotel room by her husband, John, a celebrity photographer on assignment in Tokyo. Charlotte is unsure of her future with John as she feels he is more interested in his celebrity models, particularly an American actress named Kelly, than her. Bob's own 25-year marriage is tired as he goes through a midlife crisis.
Anna Leonowens (Jodie Foster) is a British widow who has come to Siam with her son Louis (Tom Felton) to teach English to the dozens of children of King Mongkut (Chow Yun-fat). She is a strong-willed, intelligent woman, and this pleases the King, who wants to modernize his country to keep it safe from the threat of colonialism, while protecting many of the ancient traditions that give Siam its unique identity. The King and Anna discuss the differences between Eastern and Western love, and the King dismisses the notion that a man can be happy with only one wife. In order to win the favors of Britain, the King orders a sumptuous reception and delegates Anna to organize it. During the reception, the King verbally spars graciously and wittily with Sir Mycroft Kincaid (Bill Stewart), of the East India Company, who accuses Siam of being a superstitious nation. At the end of the reception, the King dances with Anna.
When stroke victim Violet Kellty dies in her isolated cabin in the North Carolina mountains, Dr. Jerome "Jerry" Lovell (Liam Neeson), the town doctor, finds a terrified young woman (Jodie Foster) hiding in the rafters of the house. She speaks angrily and rapidly but seems to have a language of her own. Looking at Violet's Bible, Jerry finds a note asking whoever finds it to look after the woman, who is Violet's daughter Nell. Sheriff Todd Peterson (Nick Searcy) shows Jerry a news clipping from which Jerry surmises that Nell is indeed the dead woman’s daughter, conceived through rape.
In 1965, Glenn Holland (Richard Dreyfuss) is a professional musician and composer who has been relatively successful in the exhausting life of a musician. However, in an attempt to enjoy more free time with his young wife, Iris (Glenne Headly), and to enable him to compose a piece of orchestral music, the 30-year-old Holland accepts a high school teaching position.
A Boston couple, Gail (Meryl Streep) and Tom (David Strathairn), are having marital problems, due to his inability to spend time with his family because of his work as an architect. She, a water rafting expert, decides to take their son, Roarke (Joseph Mazzello), on a holiday rafting trip down the Salmon River in Idaho, along with their dog, Maggie. Their daughter, Willa (Stephanie Sawyer), accompanies them to Gail's parents' house in Idaho. At the last minute, just when they are about to leave for the almost week-long trip, Tom joins them. As they are setting off, they meet a couple of other rafters, Wade (Kevin Bacon) and Terry (John C. Reilly), who appear to be friendly. Thus they leave for the trip, leaving Willa behind to be taken care of by her grandparents.
Set in the fictional town of Thayer, Massachusetts, the story focuses on Meredith Morton (Sarah Jessica Parker), a successful Manhattan executive whose uptight, conservative demeanor is a sharp contrast to that of her boyfriend Everett Stone (Dermot Mulroney) and his liberal and rambunctious family.
Kate and John Coleman (Vera Farmiga and Peter Sarsgaard) are experiencing strains in their marriage after their third child was stillborn. The loss is particularly hard on Kate, who is also recovering from alcoholism. The couple decides to adopt a 9-year-old Russian girl, Esther (Isabelle Fuhrman) from a local orphanage. While Kate's and John's deaf daughter Max (Aryana Engineer) embraces Esther immediately, their son Daniel (Jimmy Bennett) is less welcoming. Kate suspects that there might be problems in Esther's background when Esther's knowledge of sex extends beyond her age. Her suspicions deepen when Esther seriously injures another girl who had bullied her.
During World War II, USMC Cpl. Joseph F. 'Joe' Enders rallies himself to return to active duty with the aid of his pharmacist, Rita. He previously survived a gruesome battle on the Solomon Islands against the Imperial Japanese Army that killed his entire squad and left him with a scar on his neck and almost deaf in his left ear. Enders' new assignment is to protect Navajo code talker Pvt. Ben Yahzee, and carries a promotion for Enders to Sergeant. Sgt. Pete 'Ox' Anderson also receives a parallel assignment protecting Navajo code talker Pvt. Charlie Whitehorse. The Navajo code, as it was known, was a code based on two parts: 1) the Navajo language and 2) a code embedded in the language, meaning that even native speakers would be confused by it, referring to a tank as a turtle, for example. The code was close to unbreakable but also so difficult only a few people could learn it.
In 1898, Daniel Plainview, a prospector in New Mexico, mines a potentially precious ore vein from a pit mine hole. In the process of dynamiting the lode, he falls from a broken rung of the tunnel ladder and breaks his leg. He saves a silver sample, climbs out of the mine, and drags himself to the nearest assay office to record his and gets a Silver and Gold certificate claim. In 1902, he discovers oil near Los Angeles, California and establishes a small drilling company. Following the death of a worker in an accident, Daniel adopts the man's orphaned son. The boy, named H. W., becomes his nominal "business partner", allowing Daniel to paint himself to potential investors as "a family man".
In the Bélier family, sixteen-year-old Paula is an indispensable interpreter for her deaf parents and brother on a daily basis, especially in the running of the family farm. One day, a music teacher discovers her gift for singing and encourages Paula to participate in a prestigious singing contest in Paris, which will secure her a good career and a college degree. However, this decision would mean leaving her family and taking her first steps towards adulthood.
Cristina Moreno (Aimee Garcia) is applying to Princeton University. For her application essay, she tells the story of her childhood and narrates throughout the movie.
When Cole's Department Store's Santa Claus gets drunk before taking part in the Thanksgiving parade, Dorey Walker (Elizabeth Perkins), Cole's director of special events, fires him and must find a replacement immediately. She spots an old man (Richard Attenborough) berating the inebriated Santa, and begs him to take over. He introduces himself as Kris Kringle. Kris does so well during the parade that he is immediately hired to be Cole's main Santa for the holiday period. All the children in New York begin to believe that he is the real Santa, with the exception of Dorey's six-year-old daughter Susan (Mara Wilson). Dorey's boyfriend, Bryan Bedford (Dylan McDermott), does his best to convince Susan to believe. While being babysat one night by Kris, Susan shares with him her Christmas wish, she would like a dad, a house (used every year for the Cole's catalogue photoshoot) and a baby brother. Kris asks if she would begin to believe in Santa if she got all those things. Susan agrees that she would.
Agent 11 is a crime-fighting bullmastiff used by the FBI; he partners with his master Murdoch in Seattle. As they go after the Mafia boss, Sonny Talia, the dog attacks him and rips off one of his testicles. Talia is taken to the hospital to have it surgically replaced. As payback, he sends his two bodyguards, Gino and Arliss, out to kill Agent 11. For protection, the dog is sent to a training facility in Alaska.
Constructed as a series of chapters that take place at a turning point in each character's life, the story moves from seven years in the past to three years to two and finally arrives in the present day. Emily Friehl (Amanda Peet) and Oliver Martin's (Ashton Kutcher) first encounter is on a flight from Los Angeles to New York City, during which they join the mile high club. He has hopes of becoming an Internet entrepreneur and, certain of his future success, gives her his mother's phone number and suggests she call him in six years to see if his prediction came true.