Docter began working on the story in 2004, which was based on fantasies of escaping from life when it becomes too irritating. He and eleven other Pixar artists spent three days in Venezuela gathering research and inspiration. The designs of the characters were caricatured and stylized considerably, and animators were challenged with creating realistic cloth. The floating house is attached by a varying number between 10,000 and 20,000 balloons in the film's sequences. Up was Pixar's first film to be presented in Disney Digital 3-D.

Up was released on May 29, 2009 and opened the 2009 Cannes Film Festival, becoming the first animated and 3D film to do so. The film became a great financial success, accumulating over $731 million in its theatrical release. Up received critical acclaim, with most reviewers commending the humor and heart of the film. Edward Asner was praised for his portrayal of Carl, and a montage of Carl and his wife Ellie aging together was widely lauded. The film received five Academy Award nominations, including Best Picture, making it the second animated film in history to receive such a nomination, following Beauty and the Beast (1991).

Plot
Young Carl Fredricksen (Jeremy Leary) is a shy, quiet boy who idolizes renowned explorer Charles F. Muntz. He is saddened to learn, however, that Muntz has been accused of fabricating the skeleton of a giant bird he had claimed to have discovered in Paradise Falls, Venezuela, and was publicly disgraced. Muntz vowed to return to Paradise Falls and not leave until he had captured a specimen alive to clear his name.

One day, Carl befriends an energetic and somewhat eccentric tomboy named Ellie (Elie Docter), who is also a Muntz fan. She confides to Carl her desire to move her "clubhouse" – an abandoned house in the neighborhood – to a cliff overlooking Paradise Falls, making him promise to help her. Carl and Ellie eventually get married and grow old together in the restored house, working as a toy balloon vendor and a zookeeper respectively. After suffering a miscarriage and being told they cannot have more children, the two decide to realize their dream of visiting Paradise Falls. They try to save up for the trip, but repeatedly end up spending the money on more pressing needs. Finally, elderly Carl Fredricksen arranges for the trip, but Ellie suddenly becomes ill and dies, leaving him alone.

Some time later, Carl (Edward Asner) is still living in their house, now surrounded by urban development, which he refuses to sell. He ends up injuring a construction worker named Steve (Danny Mann) over damage done to his mailbox. He is evicted from the house by court order due to being deemed a "public menace", and is ordered to move to a retirement home. However, Carl comes up with a scheme to keep his promise to Ellie: he turns his house into a makeshift airship, using thousands of helium balloons to lift it off its foundation. A young member of the "Wilderness Explorers" (a fictional youth organization, based on the Boy Scouts of America) named Russell (Jordan Nagai) becomes an accidental passenger, having pestered Carl earlier in an attempt to earn his final merit badge, "Assisting the Elderly".

After surviving a thunderstorm, the house lands near a large ravine facing Paradise Falls. Carl and Russell harness themselves to the still-buoyant house and begin to walk it around the ravine, hoping to reach the falls before the balloons deflate. They later befriend a tall, colorful flightless bird whom Russell names "Kevin" (Pete Docter) and then a dog named Dug (Bob Peterson) who wears a special collar that allows him to speak. Kevin leaves, much to Russell's disappointment, when it is revealed that the bird is actually female and has chicks to care for.

Carl and Russell encounter a pack of dogs led by Alpha (also Bob Peterson), and are taken to Dug's master, who turns out to be an elderly Charles Muntz (Christopher Plummer). Muntz invites Carl and Russell aboard his airship, where he explains that he has spent the years since his disgrace searching Paradise Falls for the giant bird. The time he has spent alone and concentrating only on his mission has made him extremely paranoid and mentally unstable. When Russell innocently reveals his friendship with Kevin, Muntz becomes disturbingly hostile and starts showing the flight helmets of explorers whom he has apparently murdered, believing they were all after the bird. This prompts Carl, Russell, Kevin and Dug to flee, chased by Muntz's dogs. Kevin is injured during the escape and Russell insists that they should help her reunite with her chicks. Muntz eventually catches up with them and starts a fire beneath Carl's house, forcing Carl to choose between saving his home or Kevin. Carl rushes to put out the fire, allowing Muntz to take the bird. Carl and Russell eventually reach the falls, but Russell becomes angry at Carl for letting Muntz kidnap Kevin.

Settling into his home, Carl discovers photos of their married life in Ellie's childhood scrapbook and a final note from his wife thanking him for the "adventure" and encouraging him to go on a new one. Reinvigorated, he goes to find Russell, only to see him sailing off on some balloons, propelled by a leaf blower, to rescue Kevin. Because many balloons have popped or deflated, in order to pursue Russell, Carl empties the house of furniture so it can lift off again. Once Carl has taken off, he discovers Dug hiding under the porch and willingly accepts him into his care.

Russell is captured by Muntz, but Carl boards the airship in flight and frees both Russell and Kevin, while Dug accidentally humiliates Alpha in front of the rest of the dogs and earns their respect. However, Muntz pursues them around the airship, finally cornering Dug, Kevin, and Russell inside Carl's tethered house. Carl lures Kevin out through a window and back onto the airship with Dug and Russell clinging to her back, just as Muntz is about to close in; the insane hunter leaps after them, only to entangle his foot in some balloon lines, causing him to fall to his fate. Snapped from its tether, the house descends out of sight through the clouds, which Carl accepts as being for the best.

Carl, Russell and Dug reunite Kevin with her chicks, then fly the airship back to the city. When Russell's father misses his son's Senior Explorer ceremony, Carl proudly presents Russell with his final badge for assisting the elderly, as well as a personal addition: the grape soda cap that Ellie gave to Carl when they first met (which he dubs the "Ellie Badge"). Meanwhile, Carl's house is shown to have landed on the cliff beside Paradise Falls, as promised to Ellie.

During the credits, a series of photographs shows Carl enjoying his latest adventure: living an active life as a surrogate grandfather to Russell.

Release
When the film screened at the El Capitan Theatre in Hollywood, California from May 29 to July 23, 2009, it was accompanied by Lighten Up!, a live show featuring Disney characters. Other tie-ins included children's books such as My Name is Dug, illustrated by screenwriter Ronnie del Carmen. Despite Pixar's track record, Target Corporation and Walmart stocked few Up items, while Pixar's regular collaborator Thinkway Toys did not produce merchandise, claiming its story is unusual and would be hard to promote. Disney acknowledged not every Pixar film would have to become a franchise. Promotional partners include Aflac, NASCAR, and Airship Ventures, while Cluster Balloons promoted the film with a replica of Carl's couch lifted by hot air balloons for journalists to sit in.

Director Pete Docter intended for audiences to take a specific point from the film, saying:
Basically, the message of the film is that the real adventure of life is the relationship we have with other people, and it's so easy to lose sight of the things we have and the people that are around us until they are gone. More often than not, I don't really realize how lucky I was to have known someone until they're either moved or passed away. So, if you can kind of wake up a little bit and go, "Wow, I've got some really cool stuff around me every day", then that's what the movie's about.

Critical response
Up has met with critical acclaim. Rotten Tomatoes reports that 98% of critics have given the film a "Certified Fresh" positive review, based on 278 reviews, with an 8.6/10 review average. The site's consensus states: "Another masterful work of art from Pixar, Up is an exciting, hilarious, and heartfelt adventure impeccably crafted and told with wit and depth." The film also holds a score of 88 on the review aggregator website Metacritic. Audiences gave the film an "A+" CinemaScore.

Film critic Roger Ebert gave the film four out of four stars and called it "a wonderful film." The Hollywood Reporter lauded the film as "Winsome, touching and arguably the funniest Pixar effort ever, this gorgeously rendered, high-flying adventure is a tidy 90-minute distillation of all the signature touches that came before it." Although the San Francisco Chronicle noted that the film "contains many boring stretches of mindless freneticism and bland character interaction," it also declared that there are scenes in Up of "such beauty, economy and poetic wisdom that they belong in any anthology of great movie moments...to watch Up with any attention is to be moved and astonished by the economy with which specific visuals are invested with emotion throughout ..." Variety enthused that "Up is an exceptionally refined picture; unlike so many animated films, it's not all about sensory bombardment and volume...Unsurprisingly, no one puts a foot wrong here. Vocal performances...exude a warm enthusiasm, and tech specifications could not be better. Michel Giacchino's full-bodied, traditional score is superlative..." The Globe claimed that Up is "the kind of movie that leaves you asking 'How do people come up  this stuff?'" along with an overall positive review on the film, despite it being predictable.

The character of Carl Fredricksen has received mostly positive reception. Bill Capodagli, author of Innovate the Pixar Way, praised Carl for his ability to be a jerk and likable at the same time. Wall Street Journal editor Joe Morgenstern described Carl as gruff, comparing him to Buster Keaton, but adds that this begins to wear thin as the movie progresses. He has been compared with Spencer Tracy, an influence on the character, by The Washington Post editor Ann Hornaday and Empire Online editor Ian Freer, who describes him as similar to a "Guess Who's Coming to Dinner-era" Tracy. Entertainment Weekly editor Lisa Schwarzbaum described his appearance as a cross between Tracy and an eccentric out of a George Booth cartoon. TIME editor Richard Corliss also makes the comparison, calling him a "trash compacted version" of Tracy. He has also been compared to Walter Matthau, another inspiration for the character's design, by LA Weekly editor Scott Foundas, suggesting that actor Ed Asner was channeling him while performing the role of Carl. Variety editor Todd McCarthy described Carl as a combination of both Tracy and Matthau.

The relationship between Carl and his wife Ellie has been praised in several media outlets. In his book Disney, Pixar, and the Hidden Message of Children's Films, author M. Keith Booker described the love between Carl and Ellie as touching. While also describing the scene of the two of them aging as a "masterpiece of its own kind," he was not sure how much children would appreciate the scene, commenting that his son was squirming in his seat during the scene. Reelviews editor James Berardinelli praised their relationship, stating that it brought a tear to his eye in a way no animated film has done, including anything by famed anime director Hayao Miyazaki. Ann Hornaday praised the prologue, describing it as "worthy of Chaplin in its heartbreaking poignancy." Chicago Tribune editor Michael Phillips praised the scene, describing it as an emotional and cinematic powerhouse, and that he also was nearly moved to tears. However, Salon.com editor Stephanie Zacharek criticized the love between Carl and Ellie, describing their marriage as resembling a dental adhesive commercial more than a real relationship.

Edward Asner was praised in several media outlets for his portrayal of Carl. San Francisco Chronicle editor Mick LaSelle praised Asner as a great choice due to having a grumpiness to his voice that is not truly grumpy, but rather coming from a protective stance. Entertainment Weekly editor Lisa Schwarzbaum praised Asner's acting, stating that he has a "Lou Grant authority" to his voice. Time editor Richard Corliss stated that Asner had the "gruffness and deadpan comic timing to bring Carl to life." The Boston Globe editor Ty Burr concurred with this, stating that his Lou Grant-like voice had not diminished with time. USA Today editor Claudia Puig praised Asner's delivery, describing it as superb.

Box office
Up earned $293,004,164 in the United States and Canada, and $438,338,580 in other territories, for a worldwide total of $731,342,744. Worldwide, it is the sixth highest-grossing film of 2009, the third highest-grossing Pixar film, and the 10th highest-grossing animated film.

In the United States and Canada, Up is the 47th highest-grossing film, the tenth highest-grossing Disney film, the seventh highest-grossing 3-D film, the sixth highest-grossing animated film, the fifth highest-grossing film of 2009, and the third highest-grossing Pixar film. On its opening weekend, it performed stronger than analysts had been expecting, ranking number one with $68,108,790. This is the fourth highest-grossing opening for Pixar and the third largest post-Memorial Day opening. It set a record for opening weekend grosses originating from 3-D showings with $35.4 million (first surpassed by Avatar). The opening weekend audience was 53% female and 47% under 17 years old. The film experienced small drop-offs on subsequent weekends, but lost first place to The Hangover.

Outside the US and Canada, it is the 43rd highest-grossing film, the tenth highest-grossing animated film, the fifth highest-grossing film of 2009, and the third highest-grossing Pixar film. It was on top of the overseas box office for three consecutive weekends and four in total. Its highest-grossing opening weekends were recorded in France and the Maghreb region ($8.88 million), the UK, Ireland and Malta, ($8.44 million) and Japan ($7.24 million). These three were also its highest-grossing countries in total earnings. Among major countries, it was the highest-grossing animated film of 2009 only in Spain ($37.1 million) and Australia ($25.3 million).

Accolades
Up won two awards at the 82nd Academy Awards, for "Best Animated Feature" and "Academy Award for Best Original Score". It is the second of three animated features to have been nominated for the Academy Award for Best Picture. Beauty and the Beast and Toy Story 3 were also nominated for Best Picture in their respective years. 'Up' also won "Best Original Score", and "Best Animated Feature Film" at the 67th Golden Globe Awards. It was nominated for nine Annie Awards in eight categories, winning two awards for "Best Animated Feature" and "Best Directing in a Feature Production". Up also received the Golden Tomato from Rotten Tomatoes for highest rating feature in 2009, and best reviewed animated film, with an approval of 98 percent from film critics, based on 259 reviews. At the 2010 Kids' Choice Awards the film won "Favorite Animated Movie". Dug, the talking canine, was awarded the Palm Dog Award by the British film critics as the best canine performance at Cannes Film Festival, winning over the fox from Antichrist and the black poodle from Inglourious Basterds.