These are most common in offices, due to high machine and ink costs. Using lasers, an image of the page to be printed is made on a cylinder: wherever the laser hits it, a slight electric charge is left.
Instead of liquid ink, laser printers actually use toner, a powdered ink, which is attracted to the charged areas on the cylinder. The paper is given an opposite electrical charge so the toner sticks to the paper.
Finally the paper is heated, melting the toner onto the page. The result is usually sharper than that produced by inkjet printers. They are also normally much faster and total printing costs tend to be lower.