Electrochromic oxide films form the basis of "smart windows", which are of much interest in forthcoming building technology and are able to provide energy efficiency and indoor comfort simultaneously. This paper introduces "smart windows" technology, which now seems ready for large-scale applications. Electrochromics is discussed from the viewpoints of materials, device design, low-cost manufacturing, and applications to buildings as well as some niche products. Finally there are some perspectives on the future role of oxide electrochromics in the built environment.