Photocomposition (or phototypesetting) is one technology for creating paste ups, which are used in printing characters. Early printing technology involved the assembly of movable type, metal pieces upon which characters had been carved individually, and then either directly applying ink to that type and printing with it, or using that type to produce a stereotype, which was then used for the printing. With this technique, one must prepare type for all of the characters. In addition, if one changes font or size, movable type must be prepared for those characters as well. As a result, printers had to have a massive collection of type available at all times. Photocomposition was developed to address this inconvenience. The principle of the technology is this: light would be projected through a character board; that image could then be magnified or reduced using lenses, generating characters on printing paper or film using photographic principles. Compared to physical type, it is easy to adjust the size and spacing of characters, as well as setting them in Italic or narrow styles, using light to adjust the image of the character. Changes in font simply require exchanging the character board. For these reasons, photocomposition was the main technique for typesetting in the 1970s and 1980s.

Photocomposition machines were designed around 1910 in Europe and the United States, but the first one put into actual practice was the Japanese photocomposition machine built by Ishii Mokichi and Morisawa Nobuo in 1924 in Japan. These early manual photocomposition machines, on which the positioning and spacing of characters was done by hand, were later superseded by automatic photocomposition machines, which used computers to easily position and space characters automatically. These were then superseded by the digital typesetting used today, in which characters are produced and managed as collections of small dots.

Today typesetting is primarily done using DTP, in which individuals use computers with typesetting applications to produce printed documents; photocomposition is limited to certain types of printed matter. With DTP, the designer him or herself composes the type, checking the work as it progresses on the computer screen; in the past, typesetting instructions were given to the operator, who would then give a printed sheet to the designer, who might then have to cut and paste adjustments to the paste up. Though DTP does have the advantage of allowing easy adjustments to typesetting, it also leaves the entire job to the designer, forcing them to have a greater level of expertise about typesetting than in the past.