We propose a carbon-based counter electrode for electrochromic windows (ECWs). The electrochemical durability of carbon materials has been verified in practical applications such as commercially available electrical double-layer capacitors, and the proposed counter electrode can store charges in an electric double layer irrespective of their charge polarities. The latter factor is expected to enhance the durability of ECWs, especially against UV exposure. ECWs fabricated with the electrode have been confirmed to have potentially high durability. Some results of durability tests undertaken on electrochromic (EC) test cells and ECWs for vehicles are summarized. We also considered the possibility of the occurrence of intercalation at the carbon-based counter electrode in the coloring process using Raman scattering spectroscopy, which indicated that the electrical charge was stored at the carbon-based counter electrode in the coloration reaction by forming electric double layers, not by the intercalation of ClO4- ions. (C) 2003 Elsevier B.V All rights reserved.