Forward biasing of transparent nanocrystalline TiO2 (anatase) films in lithium ion-containing organic electrolytes leads to rapid and reversible coloration due to electron accumulation and Li+ intercalation in the anatase lattice. Absorption of >90% light throughout the visible and near IR can be switched on and off within a few seconds. The nanocrystalline morphology of the film plays a primary role in enhancing the electrochromic process.