We review data on transparent and electrically conducting films of ITO (i.e. In2O3:Sn). A survey is given on the most recent progress, in 2001, of fundamental electronic bandstructure, techniques to boost the conductivity, and alternative dopants and manufacturing techniques. We then outline quantitative theories for the optical properties and their applications. Finally, we consider ITO films for uses in optimized electrochromic window coatings capable of yielding indoor comfort and energy efficiency.