Polymeric gel electrolytes based on PMMA have high transmission in the visible region. This property along with their high conductivity and good adhesive proper ties make these materials most attractive for electrochromic window applications. Liquid electrolytes were prepared by dissolving lithium imide (LiN(CF3SO2)(2)) in propylene carbonate (PC), ethylene carbonate (EC), gamma -butyrolactone (gamma -BL) and their binary mixtures and room temperature conductivity exceeding 10(-2) S/cm has been obtained. The gel electrolytes prepared by the addition of PMMA to these liquid electrolytes resulted in large increase in viscosity without lowering the conductivity significantly. Incorporation of these gels in electrochromic devices show excellent performance characteristics making them very promising materials for window applications.