A cel, short for celluloid, is a transparent sheet on which objects are drawn or painted for traditional, hand-drawn animation. Celluloid was used for animation and film production up until the late 20th century, however, it burned easily and suffered from spontaneous decomposition, and was largely replaced by cellulose acetate plastics.

Generally, the animation characters are drawn on cels and laid over a static background drawing. This reduces the number of times an image has to be redrawn and enables studios to split up the production process to different specialised teams. Using this assembly line way to animate has made it possible to produce films much more cost-effectively. The invention of the technique is generally attributed to Earl Hurd, who patented the process in 1914. The outline of the images are drawn on the back of the cel. The colors are also painted on the back to eliminate brushstrokes. Traditionally, the outlines were hand-inked but now they are almost exclusively xerographed on. Another important breakthrough in cel animation was the development of the Animation Photo Transfer (APT) process, first seen in The Black Cauldron, released in 1985.

With the advent of computer assisted animation production, the use of cels has been practically abandoned in major productions. Disney stopped using cels in 1990 when Computer Animation Production System (CAPS) replaced this element in the animation process.

Production cels were sometimes sold after the animation process was completed. More popular shows and movies demanded higher prices for the cels, with some selling for thousands of dollars.

Some cels are not used for actual production work, but may be a "special" or "limited edition" version of the artwork, sometimes even printed ("lithographed") instead of hand-painted. These normally do not fetch as high a price as original "under-the-camera" cels, which are true collector's items. Some unique cels have fetched record prices at art auctions. For example, a large "pan" cel depicting numerous characters from the finale of Who Framed Roger Rabbit sold for $50,600 at Sotheby's in 1989, including its original background.

Disney Stores sold production cels from The Little Mermaid (their last film to use cels) at prices from $2,500 to $3,500, without the original backgrounds. Lithographed "sericels" from the same film were $250, with edition sizes of 2,500–5,000 pieces.

"I have come to Hollywood and am in touch with the three great American surrealists -- the Marx Brothers, Cecil B. DeMille and Walt Disney," the artist wrote to his friend Andre Breton in 1937. Salvador Dali had a great admiration for Walt Disney and wanted to create a movie with him. Dali approached Disney at a dinner party at the house of Warner Brothers head Jack Warner to present his idea of what he called "the first motion picture of the Never Seen Before."

Disney agreed and the result was a short film called Destino. Disney assigned director John Hench to help Dalí turn the Mexican ballad "Destino," by Armando Dominguez, into a kind of music video.