Electrically activated switchable glazing and their use as smart windows and other large-area applications are discussed. Electrochromic devices are compared to dispersed liquid crystals and dispersed particle glazing systems. A selection of device structures and performance characteristics are compared. A disctlssion of transparent conductors is presented. The characteristics of prototype and commercial devices from commercial and university labs in Japan, Europe, Australia, and USA are covered. A discussion of thesfuture of this technology is made including areas of necessary development for the realization of devices in excess of 1 m2.