The Mergenthaler Linotype Company is a corporation founded in the United States in 1886 to market the Linotype machine, a system to cast metal type in lines (linecaster) invented by Ottmar Mergenthaler. It became the world's leading manufacturer of book and newspaper typesetting equipment; outside North America, its only serious challenger for book typesetting was the Anglo-American Monotype Corporation.

The Linotype machine is a "line casting" machine used in printing which is manufactured and sold by the former Mergenthaler Linotype Company and related companies. It was a hot metal typesetting system that cast lines of metal type for one-time use. Linotype became one of the mainstays for typesetting, especially small-size body text, for newspapers, magazines, and posters from the late 19th century to the 1970s and 1980s, when it was largely replaced by phototypesetting and digital typesetting. The name of the machine comes from producing an entire line of metal type at once, hence a line-o'-type. It was a significant improvement over the previous industry standard of letter-by-letter manual typesetting using a composing stick and shallow subdivided trays, called "cases".