Dynamic windows, which switch between transparent and opaque states upon application of a voltage, have applications in buildings, automobiles, and switchable sunglasses. Here, we describe dynamic windows based on the reversible electrodeposition of Cu and a second metal on transparent indium tin oxide electrodes modified by Pt nanoparticles. Three-electrode cyclic voltammetry experiments reveal that the system possesses high Coulombic efficiency (99.9%), indicating that the metal electrodeposition and stripping processes are reversible. Two-electrode 25-cm 2 windows without bus bars uniformly switch between a transparent state ($80% transmission) and a colorneutral opaque state (<5% transmission) in less than 3 min. These devices switch at least 5,500 times without degradation of optical contrast, switching speed, or uniformity. Taken together, these results indicate that dynamic windows based on reversible metal electrodeposition are a promising alternative to those using traditional electrochromic materials.