The villain Charles Muntz's name is a nod to Charles Mintz, the Universal Pictures executive who in 1928 took the rights to Walt Disney's 'Oswald the Lucky Rabbit' cartoon series. This event pushed Disney to create Mickey Mouse, who would soon overshadow Oswald.
All the characters are based on circles and rectangles, while the villains are made of triangles. Carl and Ellie are not only composed of squares and circles; the objects around them (chairs, picture frames) are also designed to match these shapes. In a photo of them together, the frame consists of a circle and a square.
The spot where Carl and Ellie have their picnic is the same spot under the tree in A Bug's Life (1998).
Carl wears the grape soda badge seen in the Buzz Lightyear commercial in Toy Story (1995).
Pixar's tradition of referencing its next film continues here: in the room of a girl the house passes when it first lifts off, Lotso the bear from Toy Story 3 (2010), the ball from Luxo Jr. (1986) and the airplane from Toy Story (1995) can be seen.
During the marriage montage, while Ellie is painting the baby's room, she is drawing a scene from Pixar's short film Partly Cloudy (2009). This short was shown before Up in many theaters where the film played.
Dug's 'point' pose, in which his tail, back and head form a straight line, is a tribute to the pose Mickey's dog Pluto often strikes. Dug's colors also resemble Pluto's.
The aerial battle in which the dogs attack Russell with airplanes turns into a literal 'dogfight.' The dogs address each other with names like 'Grey Leader' and 'Grey One'; this is a reference to Star Wars: Episode IV - A New Hope (1977) and also a humorous nod to the myth that dogs cannot see colors. With Russell's distraction, the formation of their planes resembles the breaking up of Darth Vader's squadron during Han Solo's Death Star attack. The weapon sounds also resemble X-Wing explosions.
When Carl's house first lifts off, and in the camera pulling away from the parking lot at the end of the film, Pixar's Pizza Planet truck, known from Toy Story (1995), can be seen.
In the opening scene, while Ellie is in the hospital, there are craft supplies such as tape and colored pencils on the nightstand; this indicates that she is working on the adventure book. Carl also catches the balloon cart just as it is about to float away.
The term 'A113' is the number of the courtroom and appears on the gold plaque next to Carl as he waits to be called (Courtroom A113). A113 is a frequently used Pixar inside joke based on one of the room numbers of the animation program at Cal Arts.
When we first see Carl as a child, the left side of his collar is outside his vest and the right side is inside. When we first see Russell, the left side of his collar is under his neckerchief and the right side is out.
Russell's Wilderness Explorer sash contains many inside jokes and tributes. The most obvious is the Luxo Jr. (1986) ball, which can also be seen on the floor of the room of a girl watching Carl's house float by. On one badge there is a hamburger with a candle in it; this is a nod to Merritt Bakery in Oakland, the favorite spot of director Pete Docter and producer Jonas Rivera. Another badge is dedicated to 2D animation, a tribute to the perforated paper used by 2D animators. There are also First Aid and Second Aid badges; this may refer to a short on the Up website in which Russell struggles to put a bandage on Carl. Another badge depicts the multicolored pinwheel that is the 'wait' icon of Apple's Mac OS X operating system. Many of the badges are shown in the credits. An additional tribute to Apple and Steve Jobs is Russell trying to teach Carl how to use a computer. The font used for the numbers on Carl's alarm clock is 'Chicago,' one of the first fonts designed for the Macintosh.
While playing in the abandoned house, Ellie travels to Paradise Falls; with her soda-bottle binoculars she sees a puppy, and then says they are about to enter a storm with lightning and hail. Carl flies the same house to Paradise Falls using the same window; on the way they pass through a storm, and the first living creature they encounter is a puppy.
When Russell knocks on the door, Carl is watching a home shopping channel. This program became a well-known montage video in which a salesman describes a painting of a horse, but the painting is actually a moth.
In the newly updated photo album, a picture of the couple shows them looking back over their shoulders in a car (Carl in the driver's seat). Their pose and the car are a re-creation of a famous ghost photograph. In the photo, the man was posing with his new car, and the ghostly image of his mother was in the passenger seat.
Charles Muntz is the sixth Disney villain to die by falling in an animated film (after the Evil Queen in Snow White and the Seven Dwarfs, Ratigan in The Great Mouse Detective, McLeach in The Rescuers Down Under, Gaston in Beauty and the Beast and Frollo in The Hunchback of Notre Dame). He is the first Pixar villain to do so. It should also be noted that Lucifer the cat in Cinderella falls to his death but is alive in the sequel; Maleficent in Sleeping Beauty falls after being wounded by a sword; Clayton in Tarzan dies after fighting Tarzan, hanging himself in the vines; and Queen Narissa in Enchanted, although animated, dies by falling in the live-action part of the film.
As Russell passes by the airship with balloons and a leaf blower, we see several of Charles Muntz's dogs playing poker at a card table. This is a tribute to Cassius Marcellus Coolidge's famous 'Dogs Playing Poker' painting series.
One of the construction machines bears the inscription L 415-72; this is the birthday of art director Lou Romano.
The ancient sword Muntz holds against Carl is a Claymore, like William Wallace's famous sword.
There are interesting parallels between Charles Muntz and Charles Lindbergh: both share the name Charles, both were celebrated explorers, and both disappeared from the public eye after becoming figures of ridicule; both were aviators who used airships named 'Spirit'.
The victory music when Dug defeats Alpha and puts the cone of shame on him recalls the music from the scene in Finding Nemo where Nigel defeats the seagulls.
Carl's summons has the zip code 94070; this is the zip code of San Carlos, where producer Bradford Lewis was once mayor.
In the credits, Carl takes Russell to see Star Wars; Disney later acquired Lucasfilm in 2012, bringing the entire Star Wars series under its umbrella.
One of Carl's Paradise Falls brochures contains an image based on the Sunny Miami figure from Knick Knack.
The opening newsreel introduces Muntz's dogs and technology; when the dogs first appear in South America, their talking collars give an early hint as to who their master is.
'Shady Oaks Retirement Village' in the brochure may be a reference to the 'Shady Pines' retirement home in The Golden Girls.
The round red lights on the dogs' collars evoke HAL 9000 in 2001: A Space Odyssey.
The bird Russell names 'Kevin' was named after Kevin Spacey, who voiced Hopper in A Bug's Life.
Up is the second Pixar film in which a protagonist loses a loved one; the first was Finding Nemo.
Throughout the film, the word 'up' is spoken only eleven times.
It is Pixar's second film with a protagonist who breaks the law; the first was Cars.
The music in the film's opening montage was used in a 2016 Save the Food.com commercial.
The film has a notorious copy: What's Up: Balloon to the Rescue! (2009).
Russell says he found a 'snipe' under Carl's house and that it 'looks like a big mouse with a long tail'; Dug later hides in the same spot.
The abandoned house where Carl and Ellie met as children is the very same house they lived in throughout their marriage and that Carl takes to Paradise Falls.
The film popularized the term 'Cone of Shame'; its official name is the Elizabethan collar or E-collar.