A dye laser uses a fluorescent organic dye in liquid solution, or in a polymer, as the active medium. The device may be excited either by a flashlamp or with a giant-pulse solid-state laser. The broad fluorescence linewidth of a dye and the large variety of dyes available permit the construction of a tunable laser operating throughout the visible spectrum. Furthermore, use of a liquid active medium facilities cooling of the laser for operation at high repetition rates. The gain and power output performance of the dye laser is greater than that of the gas laser and is comparable to that obtained from solid-state lasers. Factors which influence the gain of the dye laser and the excitation power required to reach threshold are reviewed. Tuning by means of dispersive elements in the dye laser cavity is discussed. The results of mode-locking experiments are described. Also, consideration is given to the possibility of obtaining CW operation of the dye laser.