Electrolytes play an important role in determining the performance of conducting polymer electrochromic devices. Good electrolytes should have high conductivity, large electrochemical windows, excellent thermal and chemical stability, and negligible evaporation. Room-temperature ionic liquids are ideal electrolytes to satisfy these requirements. In the present work, we explored the applications of ionic liquids as electrolytes in electrochemical synthesis of conducting polymers, in electrochemical and electrochromic characterization of both electrochemically and chemically synthesized conducting polymers and in fabrication of conducting polymer electrochromic devices. In ionic liquids, highly stable electroactivity has been obtained for polyaniline in a wide potential range covering its entire redox process of leucoemeraldine <----> emeraldine <----> pernigraniline for >1,000,000 cycles. During the fabrication of electrochromic devices, electrochemically synthesized polymers were employed for displays, while chemically synthesized polymers (via spin-coating) were preferable for large-area electrochromic windows. We have successfully fabricated the prototypes of alphanumeric displays and large-area (5 x 5 cm) electrochromic windows. High device performance of low operation voltages (<1.5 V), high coloration contrast (>50%), fast coloration speed (<100 ms), and high coulombic efficiency (>98%) has been realized. (C) 2004 The Electrochemical Society.