This video defines the general physical principles of lasers and the basic mode of action of crystal lasers. Laser-tissue interactions using Nd/YAG and CO 2 lasers are compared, and modes of delivery of various wavelengths are described. Most Nd/YAG lasers manufactured in the U.S. are shown and their systems compared. The surgical indications and application of the Nd/YAG laser in head and neck surgery are demonstrated. The difference between "contact" and "non-contact" surgical techniques are shown.