An ink cartridge is a changeable component of an ink jet printer. It contains the ink that is spread on paper during printing and sometimes the print-head itself. Each ink cartridge contains one or more partitioned ink reservoirs and certain manufacturers also add electronic contacts and a chip that communicates with the printer.

Before printing anything, the ink level must be checked. If it is too low, ink may dry on the print head and lead to low quality prints. The ink must have a smooth flow in order to produce high quality prints. To clean the dried ink from the print head, it is strongly advised to gently rub the head with isopropyl alcohol on a swab or paper towel.

In most cases, ink cartridges are very expensive. Many people prefer to use compatible ink cartridges, made by a company other than the printer manufacturer. These cartridges can sometimes match the quality, but with possible savings. Another alternative involves some modifications to allow the use of continuous ink systems that use external ink tanks. Some people even choose to use aftermarket inks. They can refill their own ink cartridge, buy aftermarket remanufactured brands, or even take them to a local refiller to refill them.

The costs of replacing ink cartridges, compared to the price of a brand new printer, amaze many of the customers. Leading printer manufacturers like Hewlett Packard, Lexmark, Dell, Canon, Epson and Brother often loose money by selling cheap printers. They must recover these losses and make a profit by selling very expensive cartridges over the life span of the printer. Because companies producing aftermarket ink cartridges take away a part of their profit, major printer manufacturers have taken action against them. Some manufacturers even took legal action.

Recently, many printer owners prefer to refill their used cartridges or even buy remanufactured cartridges from third parties rather than buying expensive new cartridges. Since they only need to buy the ink and a few other small raw materials, it is much cheaper and quality is almost the same. Customers can find different qualities and types of refilling. However, some of them can damage the printer and lead to low quality prints. People take their empty cartridges to refillers or remanufacturers, or simply buy store branded ink.

Another option is for the consumer to refill the cartridges. Instructions for most cartridges are available on the web, as well as sources who sell "bulk ink" in pints, quarts, and even gallons. This can be extremely cost effective if the consumer is a heavy user of cartridges. One pint (473 ml) is sufficient ink to fill approximately 15 to 17 large cartridges of a typical 27 ml capacity. At the price of an original cartridge, you can buy at least one pint of ink.

Brother, Canon, Dell, HP, and Lexmark cartridges ink cartridges are very easy to refill manually. By using a simple syringe, you can fill some of them. All you need is ink. However, Epson cartridges are usually hard to refill and need a chip resetter. This tool resets the counter chip inside the cartridge. Refilling process can be messy as it involves handling ink directly. Some experience is needed to make the process as clean as possible.

Laser/toner cartridges sold as "compatible" are usually re-filled cartridges, although many third-party newly manufactured cartridges exist. Inkjet cartridges sold as "compatible" are newly manufactured cartridges. Inkjet cartridges sold as "remanufactured" are cartridges that have been used at least once by a consumer and then refilled by a third party. Note that used cartridges might not work as expected.