The inkjet printer sprays tiny dots of ink at the page by applying pressure that is caused by electricity or an electrical charge. Pressure inside the ink reservoir of the cartridge is less than the outside pressure until the electricity is applied, then the pressure rises. This internal pressure causes small dots of ink to be forced out through the nozzles.

Inkjet printers have two kinds of print heads. One popular brand of inkjet printers has a type of head called a thermal-shock or bubble-jet print head. It has a heating element that surrounds each nozzle and when heated by an electrical current, it causes the ink to expand. This expansion causes the ink to be ejected through the nozzle.

Another popular brand of inkjet printer operates based on electrostatic charges. When the deflection plates are electrically charged, the size and shape of the nozzle changes, causing it to act like a pump. This pumping action forces ink through the nozzle to the paper. These print heads are called piezoelectric print heads.

Inkjet printers are designed to use plain paper, but may also be used with very specific inkjet paper when high quality print or photographs are required.

When the inkjet print operation is complete and the paper exits the printer, the ink is often still wet. Touching it can smear the ink and smudge the printout.

The quality of print for an inkjet printer is measured in dots per inch (dpi), and the print speed is measured in pages per minute (ppm).