When it was introduced in 1884, linotype represented the first major change in the mechanics of typesetting in over four hundred years. Ever since Johannes Gutenberg laid out the principles of mechanical printing in the mid-fifteenth century, European typesetters--in spite of an exponential increase in the demand for and variety of printed material--used the same laborious technique of manually constructing full pages of type out of pre-made metal casts of letters. Whereas printers once had to cast type by hand, linotype allowed them to create mechanically customized type, one "line of type" at a time.

Previous attempts at speeding up the typesetting process involved using human hands, rather than machines, to set the full pages of type, but none of these attempts was very successful. However, Ottmar Mergenthaler, the inventor of linotype, discarded the idea of physically setting pre-made letters; his idea was to alter the printing process by building a machine that would custom-make letters to fit the needed document. In Mergenthaler's finished machine, the typesetter uses a typewriter-like device which has ninety keys to lift copper casts of letters and punctuation (called matrices) into place. Once the line is finished, a quick-cooling molten alloy is poured over the casts; when it cools, it forms a complete line of type, or "slug," which can be set into place. Linotype drastically shortened the time needed to create a page of type for the printing press, allowing typesetters to set more than five thousand pieces of type per hour, as opposed to fifteen hundred per hour by hand. A second version of the machine was able to automatically justify text by inserting spaces between words so that each line is the same width. The invention was immediately and universally popular. In 1886, The New York Tribune became the first publication to use linotype; by Mergenthaler's death in 1899, more than three thousand of the machines were in use, produced at three factories around the world. Eventually about 100,000 linotype machines were manufactured in all. Though linotype deserves credit for making possible the tremendous boom in the publishing industry during the twentieth century, by century's end the machines were supplanted by computer technology and the advent of desktop publishing.