Lasers can be used both to initiate chemical reactions and to control their rates and product distributions. The frequency, intensity, and phase properties of a laser beam are used to great advantage in controlling the motion of nuclei and electrons. For example, infrared radiation is used to excite specific vibrational modes of a molecule, whereas visible radiation and ultraviolet radiation are used to induce electronic transitions. The tunability and narrow bandwidth (that is, sharp wavelength) of a laser permit very precise selection of the desired transition. The high intensity achievable with pulsed lasers promotes multiphoton or overtone transitions. Finally, the phase coherence of a laser exploits the quantum-mechanical properties of matter in ways that are inaccessible by conventional methods.