Although everybody recognizes the strong potential of solar thermal energy to seawater desalination due to the usual coincidence of water shortage, good solar radiation level and seawater availability, the process is not yet developed at commercial level. The main reason for this is that the existing technology cannot presently compete with conventional distillation and reverse osmosis technologies. During the 90s, the Plataforma Solar de Almería developed the Solar Thermal Desalination project demonstrating the technical feasibility and high reliability of solar desalination systems combining a multi-effect distillation plant with a parabolic-trough solar collector field. Based in this previous background and experience, a new project has been initiated in 2002 with the main objective to develop a zero-discharge, improve cost- and energy-efficient seawater desalination technology based on multi-effect distillation process. First performed analysis shows that this technology could be fully competitive if the total achieved cost of the solar associated hardware is in the range of 90–155 €/m².