These intelligent windows have the capacity to regulate the passage of light to the desired extent, thanks to the use of electrochromic materials capable of darkening or brightening the interfaces, depending on the electrical potential applied to them. The materials capable of controlling the passage of light in an electronic manner may be classified, more or less, in the following three ways: liquid crystals, electrochromic materials and suspended particles devices. The CIDETEC centre has been carrying out work on electrochromic materials. How do devices using electrochromic materials (EC) work?,An EC device is a multilayer coating of very few µm thickness, and with a pure ionic conductor (electrolyte) between two layers, one of EC material and the other made up of a counter electrode. This, in turn, is inserted between two layers of a transparent electrical conductor. On applying a voltage across the transparent conductors, an electrochemical reaction is produced in which ions are inserted into or extracted from the EC layer. This gives rise to a molecular change and a modulation in the spectral dependence of the optical transmission (that is, in fact, in the colour of the material). Intelligent windows,These windows have a high laminated crystal incorporated which to which is attached a solar control film set between two PVB laminas. Its main quality lies in its ability to selectively control the suns infrared energy, thus enabling a high level of luminous transmission. These type of crystals are also useful in all kinds of crystal glass exposed to the suns rays, both for curved and flat applications: glass domes, skylights, tilted panes, automotion, trains and water craft. Also, the technology of intelligent windows has a number of advantages such as, amongst others, energy saving through reducing refrigeration in the premises, the reduction in electric power consumption for illumination and the savings on complements for solar control. CIDETEC technology centre has carried out this two-year project for an industrial client (the Catalan company, Cristales Curvados S.A.). The first intelligent windows due to be sold by this company will be launched on the market in the current year (2004).