Electrochromic materials are highly desirable because their tinting can be adjusted by a switch or automated control to allow the ideal amount of light to pass through a window a skyroof or eyeglasses. A key advantage of attenuating light with electrochromics is that the view is not distorted as it is when a curtain or blinds are used. Studies have shown that the heating and cooling costs of buildings can be reduced by 20% simply by using electrochromic materials to control the radiative transfer of heat into and out of the buildings. Several companies are trying to commercialize electrochromic windows but the technology has not yet become ubiquitous because most of the windows have a bluish tint switch slowly over approximately 20 minutes and are slightly too expensive. We have developed a completely different approach to dynamically controlling the tinting of windows that is based on a transparent electrode similar to those used in flat-panel displays and a polymer gel containing metal ions. When a voltage is applied to the electrode a thin film of metal that is capable of absorbing light forms. When the opposite voltage is applied the metal is stripped away and the transparency of the window is restored. These windows are color neutral and can be switched on and off more than 5000 times without degradation. They are simpler than electrochromics and have the potential to be cost-effective when scaled up.