Ink jet printers are the most common type of computer printer; and industry and commerce also use them extensively for special-purpose applications. For example, many ATMs, stock control systems, and cash registers use an inkjet printer.

An Epson inkjet printer

In the personal and small business computer market, inkjet printers currently easily predominate. Inkjets are usually inexpensive, quiet, reasonably fast, and many models can produce high quality output.

Like most modern technologies, the present-day inkjet has built on the progress made by many earlier versions. Among many contributors, Hewlett-Packard and Canon can claim a substantial share of credit for the development of the modern inkjet. In the worldwide consumer market, four manufacturers account for the majority of inkjet printer sales: Canon, Hewlett-Packard, Epson, and Lexmark.

Most current inkjets (Epson being a notable exception) work by having a print cartridge with a series of tiny electrically-heated chambers constructed by photolithography. To produce an image, the printer runs a pulse of current through the heating elements. A steam explosion in the chamber forms a bubble, which propels a droplet of ink onto the paper (hence Canon's tradename for its inkjets, bubblejet). When the bubble condenses, surplus ink is sucked back up from the printing surface. The ink's surface tension pumps another charge of ink into the chamber through a narrow channel attached to an ink reservoir. Epson's Micro Piezo technology uses a piezo crystal in each nozzle instead of a heating element. When current is applied, the crystal bends, forcing a droplet of ink from the nozzle.

Older ink jet printers directed ink streams electrostatically or piezoelectrically; ultrasound was used to induce waves in the ink, which then broke into little droplets that would fall on the right place on the page.

Compared to earlier consumer-oriented printers, ink jets have a number of advantages. Compared to dot matrix or daisywheel printers, they run much more quietly. Many can produce high resolutions, and color printing of excellent quality is widely available.

The disadvantages of inkjets include flimsy print heads (prone to clogging) and expensive ink cartridges (sometimes costing US$30 – $40 or more). This typically leads value-minded consumers to consider laser printers for medium-to-high volume printer applications.

Two main design philosophies operate in inkjet head design. Each has strengths and weaknesses.

The fixed-head philosophy provides an inbuilt print head that is designed to last for the whole life of the printer. The idea is that because the head need not be replaced every time the ink runs out, consumable costs are typically lower and the head itself can be more precise than a cheap disposable one. On the other hand, if the head is damaged, it is usually necessary to replace the entire printer. Epson have traditionally used fixed print heads. In fact, disposable heads have proven to be equally good.

The disposable head philosophy uses a print head which is part of the replaceable ink cartridge. Every time the printer runs out of ink, the entire cartridge is replaced with a new one. This adds to the cost of consumables and makes it more difficult to manufacture a high-precision head within reasonable cost limits, but also means that a damaged print head is only a minor problem: the user can simply buy a new cartridge. Hewlett-Packard has traditionally favoured the disposable print head, as did Canon in its early models.

A few printers (including certain Olivetti and Fujitsu models) have used an intermediate method: a disposable ink tank mounted on a disposable head, which is replaced infrequently (perhaps every sixth ink tank or so). These did not achieve great market success.

Canon now uses (in most models) replaceable print heads which are designed to last the life of the printer, but can be replaced by the user if they should become clogged. The ink tanks are separate for each ink color.

A common business model for ink jet printers involves selling the actual printer at or even below cost, while dramatically marking up the price of the (proprietary) ink cartridges. Hewlett-Packard, for example were recently able to cover the entire 12-month losses accumulated by their other division with the profits made by their consumables division, and have a little left over.

Alternatives for consumers are cheaper copies of cartridges, produced by other companies, and refilling cartridges themselves, for which special refill sets are for sale. As a result of the large differences in pricing due to OEM markups, there are many companies specializing in these types of alternative off-brand ink cartridges.

Some inkjet printers use microchips in the cartridges to prevent the use of third-party or refilled ink cartridges. The E.U. ruled this practice illegal: it will disappear in newer models.

High-end inkjet printers can be used to produce fine-art prints called giclées.