Lithography - Litho - is a method in printing business works using a plate or stone with a completely smooth surface. By contrast, in intaglio printing plate is engraved (engraving), etched (etching) or stippled (mezzotint) to make cavities to contain the printing ink, and in woodblock printing and letterpress ink is applied to the raised surfaces of letters or images.

Lithography uses oil or fat and gum arabic to divide the smooth surface into hydrophobic regions which accept the ink, and hydrophilic regions which reject it and thus become the background. Invented by Bavarian author Alois Senefelder in 1796, it can be used to print text or artwork onto paper or another suitable material.

Most books, indeed all types of high-volume text, are now printed using offset lithography, the most common form of printing production. The word "lithography" also refers to photolithography, a microfabrication technique used to make integrated circuits and micro electro mechanical systems, although those techniques have more in common with etching than with lithography.

Lithography uses chemical processes to create an image. For instance, the positive part of an image would be a hydrophobic chemical, while the negative image would be hydrophilic. Thus, when the plate is introduced to a compatible printing ink and water mixture, the ink will adhere to the positive image and the water will clean the negative image. This allows a flat print plate to be used, enabling much longer and more detailed print runs than the older physical methods of printing (e.g., intaglio printing, Letterpress printing).

The plate is affixed to a cylinder on a printing press. Dampening rollers apply water, which covers the blank portions of the plate but is repelled by the emulsion of the image area. Ink, which is hydophobic, is then applied by the inking rollers, which is repelled by the water and only adheres to the emulsion of the image area--such as the type and photographs on a newspaper page.

If this image were directly transferred to paper, it would create a negative image and the paper would become too wet. Instead, the plate rolls against a cylinder covered with a rubber blanket, which squeezes away the water,picks up the ink and transfers it to the paper with accurate pressure. The paper rolls across the blanket drum and the image is transferred to the paper. Because the image is first transferred, or offset to the rubber drum, this reproduction method is known as offset lithography or offset printing .

Many innovations and technical refinements have been made in printing processes and presses over the years, including the development of presses with multiple units (each containing one printing plate) that can print multi-color images in one pass on both sides of the sheet, and presses that accommodate continuous rolls (webs) of paper, known as web presses.

Another innovation was the continuous dampening system first introduced by Dahlgren instead of the old method which is still used today on older presses (conventional dampening), which are rollers covered in molleton (cloth) which absorbs the water. This increased control over the water flow to the plate and allowed for better ink and water balance. Current dampening systems include a "delta effect or vario " which slows the roller in contact with the plate, thus creating a sweeping movement over the ink image to clean impurities known as "hickies".

The advent of desktop publishing made it possible for type and images to be manipulated easily on personal computers for eventual printing on desktop or commercial presses.

The development of digital imagesetters enabled print shops to produce negatives for platemaking directly from digital input, skipping the intermediate step of photographing an actual page layout.

The development of the digital platesetter in the late twentieth century eliminated film negatives altogether by exposing printing plates directly from digital input, a process known as computer to plate printing.