The increase in the interaction between man and machine has made display devices indispensable for visual communication. The information which is to be communicated from a machine can be often in the form of color images. Electrochromic display device (ECD) is one of the most powerful candidate for this purpose and has various merits such as multicolor, high contrast, optical memory, and no visual dependence on viewing angle. A large number of electrochromic materials are available from almost all branches of synthetic chemistry. In this review, we have tried to describe the fundamentals of such electrochromic materials and their use in EDDs. The most important examples from major classes of electrochromic materials namely transition metal oxides, Prussian blue, phthalocyanines, viologens, fullerenes, dyes and conducting polymers (including gels) are described. Examples of their use in both prototype and commercial electrochromic devices are given. (C) 2002 Elsevier Science B.V. All rights reserved.