Two examples of all solid state and flexible electrochromic devices assembled under atmospheric conditions are described. The devices were constructed using polypyrrole and polythiophene derivatives as electrochromic materials, deposited on optically transparent plastic electrodes. An elastomer, poly(epichlorohydrin-co-ethylene oxide) containing LiClO4, was used as electrolyte. Results indicated that the systems present high optical contrast in the visible range and fast optical response times. We also discuss some strategies to enhance the optical contrast and optical response time of conducting polymers used in electrochromic devices.