The optical performance of Li‐based variable transmission electrochromic windows incorporating tin‐doped indium oxide thin‐film counterelectrodes have been measured. The electrolyte used was 1M LiClO4dissolved in dry propylene carbonate, the active device area was approximately 10 cm2and the devices were driven galvanostatically with a current density of 100 or 200 &mgr;A/cm2. Significant and reversible transmission modulation could be achieved in these devices. The characteristics of the WO3electrochromic electrode and the tin‐doped indium oxide counterelectrode used were found to have a marked effect on the optical response of the device. The plasma wavelength of the tin‐doped indium oxide counterelectrode was found to be a critical parameter.