W oxide films are of critical importance for electrochromic device technology, such as for smart windows capable of varying the throughput of Visible light and solar energy. This paper reviews the progress that has taken place since 1993 with regard to him deposition, characterization by physical and chemical techniques, optical properties, as well as electrochromic device assembly and performance. The main goal is to provide an easy entrance to the relevant scientific literature. (C) 2000 Elsevier Science B.V. All rights reserved.