Encouraged to explore as a child by her late father, Dr. Eleanor "Ellie" Arroway works for the Search for Extraterrestrial Intelligence (SETI) program at the Arecibo Observatory in Puerto Rico. She listens to radio transmissions hoping to find signals sent by extraterrestrial life. Science Advisor to the President David Drumlin pulls the funding from SETI because he believes the endeavor is futile. Arroway gains backing from secretive billionaire industrialist S. R. Hadden, who has followed her career and allows her to continue her studies at the Very Large Array (VLA) in Socorro County, New Mexico.
In early September, 1962, recent high school graduates and longtime friends, Curt Henderson and Steve Bolander, meet John Milner and Terry "The Toad" Fields at the local Mel's Drive-In parking lot. Despite receiving a $2,000 scholarship from the local Moose lodge, Curt is undecided if he wants to leave the next morning with Steve to go to the northeastern United States to begin college. Steve lets Toad borrow his 1958 Chevrolet Impala for the evening and while he's away at college. Steve's girlfriend, Laurie, who also is Curt's sister, is unsure of Steve's leaving, to which he suggests - to Laurie's surprise - they see other people while he is away to "strengthen" their relationship. She is not happy with his proposal.
In 1965, Airman Second Class Adrian Cronauer (Williams) arrives in Saigon from Crete to work as a DJ for Armed Forces Radio Service. Cronauer is greeted by Private First Class Edward Montesquieu Garlick (Whitaker). Cronauer's irreverence contrasts sharply with many staff members and soon rouses the ire of two of his superiors, Second Lieutenant Steven Hauk (Kirby) and Sergeant Major Phillip Dickerson (Walsh). Hauk adheres to strict Army guidelines in terms of humor and music programming, while Dickerson is generally abusive to all enlisted men. However, Brigadier General Taylor (Willingham) and the other DJs quickly grow to like the new man and his brand of comedy. Cronauer's show consists of unpredictable humor segments mixed with news updates (vetted by the station censors) and rock and roll records that are frowned upon by his superiors.
A car delivery driver, Kowalski (Barry Newman), arrives in Denver, Colorado late Friday night with a black Chrysler Imperial. The delivery service clerk, Sandy (Karl Swenson), urges him to get some rest, but Kowalski insists on getting started with his next assignment to deliver a white 1970 Dodge Challenger R/T 440 Magnum to San Francisco by Monday. Before leaving Denver, Kowalski pulls into a biker bar parking lot around midnight to buy Benzedrine pills to stay awake for the long drive ahead. He bets his dealer, Jake (Lee Weaver), that he will get to San Francisco by 3:00 pm "tomorrow", even though the delivery is not due until Monday. (Distance between the towns is approximately 1,000 miles (1,600 km) by road).
Three convicts, Ulysses Everett McGill (George Clooney), known as Everett, Pete Hogwallop (John Turturro) and Delmar O’Donnel (Tim Blake Nelson) escape from a chain gang and set out to retrieve the $1.2 million that Everett buried. The three get a lift from a blind man driving a handcar on a railway. He tells them that they will find a fortune, but not the one they seek. The trio make their way to Pete’s cousin Wash’s house. They remove their chains and sleep in the barn, but Wash betrays them and they are woken by policemen led by Sheriff Cooley, who have them surrounded. The police try to smoke them out, but Wash’s son rescues them.
On February 1, misanthropic TV meteorologist Phil Connors (Bill Murray), news producer Rita Hanson (Andie MacDowell), and cameraman Larry (Chris Elliott) of the fictional Pittsburgh television station WPBH-TV 9 travel to Punxsutawney, Pennsylvania, to cover the annual Groundhog Day festivities. The following morning, Phil, who does not like the assignment or Punxsutawney, grudgingly gives his report on the festivities. He then gets his team on the road back to Pittsburgh, but a blizzard shuts down all travel. The team is forced to return to Punxsutawney and stay another night.
As radio show host Erica Bain (Jodie Foster) and her fiancé David (Naveen Andrews) are walking their dog at night at Stranger's Gate in New York's Central Park, they are attacked by three violent criminals who film the whole attack on their phones. David dies from his injuries, and Erica, while seriously injured, survives. Angry and traumatized, she attempts to purchase a gun. Terrified and unwilling to wait the month required to obtain a gun legally, she buys a Kahr K9 semi-automatic pistol from a black market gun dealer.
In Queens, New York during October 1999, John Sullivan (Caviezel), a 36-year-old homicide detective, breaks up with his girlfriend Samantha (Melissa Errico) with the reason partially attributed to the trauma caused by the death of his fireman father Frank (Quaid). Still living in the same house where he grew up, he discovers his father's Heathkit single-sideband ham radio and begins transmitting radio signals. Because of highly localized electro-temporal spatial effects caused by unusual aurora borealis activity, John somehow makes contact with his father exactly 30 years in the past on the day before Frank's death in a warehouse fire. The ensuing conversation results in Frank thinking John is a stalker. Before the connection cuts out, John is able to shout out the circumstances that led to Frank's death. The next day as little things brought up in their conversation prove true, Frank believes and heeds John's words, escaping the fire to safety. The father and son reconnect on the HAM radio set later that evening, with Frank sharing his dreams and his hopes for his son, and John recounting the details of the Mets-Orioles World Series, which is just beginning in Frank's timeline in 1969. John also reveals to Frank that he now dies of lung cancer in 1989 due to his smoking habit.
The movie is filmed in the style of a docudrama. Beginning in the days leading up to D-Day, it concentrates on events on both sides of the channel, such as the Allies waiting for the break in the poor weather and anticipating the reaction of the Axis forces defending northern France. The film pays particular attention to the decision by Gen. Eisenhower, supreme commander of SHAEF, to go after reviewing the initial bad-weather reports as well as reports about the divisions within the German High Command as to where an invasion might happen or what the response to it should be.
Jack Lucas (Bridges), a selfish, misanthropic shock jock, becomes suicidally despondent after his insensitive on-air comments inadvertently prompt an unstable caller to commit a mass murder-suicide at a popular Manhattan restaurant. Three years later, Jack is working with his girlfriend Anne (Ruehl) in a video store in a mostly drunken, depressed state. One night while on a bender, he attempts suicide. Before he can do so, he is mistaken for a homeless person and is attacked and nearly set on fire by thugs. He is rescued by Parry (Williams), a deluded homeless man who is on a mission to find the Holy Grail, and tries to convince Jack to help him. Jack is initially reluctant, but comes to feel responsible for Parry when he learns that the man's condition is a result of witnessing his wife's horrific murder at the hands of Jack's psychotic caller. Parry is also continually haunted by a hallucinatory red knight, who terrifies him.
In 1966, numerous pirate radio stations broadcast to the United Kingdom from ships anchored in international waters, specialising in rock and pop music that is not played on BBC Radio. Seventeen-year-old Carl (Tom Sturridge), recently expelled from school, is sent to stay with his godfather Quentin (Bill Nighy), who runs the station "Radio Rock" anchored in the North Sea. The eclectic crew of disc jockeys and staffers, led by the brash American DJ "The Count" (Philip Seymour Hoffman), quickly accept Carl as one of their own.
A man calling himself Henry Faber is actually a German spy nicknamed "the Needle" because of his preferred method of assassination, the stiletto. He is a coldly calculating sociopath, emotionlessly focused on the task at hand, whether the task is to signal a U-boat or to gut a witness to avoid exposure.
Joe (Woody Allen), the narrator, explains how the radio influenced his childhood in the days before TV. The young Joe (Seth Green) lives in New York City in the late 1930s and early 1940s. The tale mixes Joe's experiences with his remembrances and anecdotes, inserting his memories of the urban legends of radio stars, and is told in constantly changing plot points and vignettes.
Dave Garver (Clint Eastwood) is a KRML radio jockey who broadcasts nightly from a studio in Carmel-by-the-Sea, California, often incorporating poetry into his program. He lives a rather freewheeling bachelor lifestyle. At his favorite bar, seemingly by coincidence, he encounters a woman named Evelyn Draper (Jessica Walter). Dave drives Evelyn home, where she reveals that their meeting was not coincidental; she deliberately sought him out after hearing the bar mentioned on his radio show. He guesses correctly that she is a recurring caller who always requests the jazz standard "Misty." The two have sex.