Despite the advantages of solar membrane distillation (MD) systems very few experimental systems have been developed as opposed to the mature technologies solar PV-driven RO and solar distillation. Therefore, main objective of MEDESOL Project is the development of an environmentally friendly improved-cost desalination technology to fresh water supply in arid and semi-arid regions in EU and Third Countries based on solar MD. The layout involves the innovative concept of multistage MD in order to minimize specific energy and membrane area required and also to substantially reduce the brine generation. The system is developed to be driven by the most energy-efficient and cost-effective solar collectors at suitable working temperature, compound parabolic concentrators. The aim of this work was to evaluate the technical feasibility of producing potable water from seawater by integrating several membrane distillation modules (Multi-step Membrane Distillation System). The aim is to develop systems for a capacity ranging from 0.5 to 50 m3/day. Technical simplicity, long maintenance-free operation periods and high-quality potable water output are the very important aims which will enable successful application of the systems that are based in membrane distillation. The heat source will proceed from an advanced compound parabolic solar concentrator, developed to the specific concentration ratio to achieve the specific needed range of temperatures (90ºC) and the seawater heater will include the development of an advanced non-fouling surface coatings to avoid the deposit formation (i.e. scaling) at such temperature. Laboratory tests under defined testing conditions of all components are very important for the preparation of successful field tests under real conditions. The development of such a solar desalination technology will involve the following phases: 1. Design and construction of the three prototypes form multi-stage MD concept development: multiple MD units and modified-design of compound solar static collector optimised for MD application. 2. Preliminary test with saline solutions of the solar-thermal driven MD technology by connecting the multistage MD system to an existing solar collector field at project coordinator facilities and experimental testing of above solar collector prototype. 3. Development, testing and assessment of two different MD system prototypes the UE and Third (Developing) Countries respective scenarios regarding the initial test previously conducted. 4. Final design of pre-commercial systems for UE and Developing Countries respective scenarios and techno-economic and environmental assessment of the developed technology in comparison with other desalination technologies driven by solar and conventional energies. MEDESOL three systems to be constructed and tested: a) MEDESOL-1: First preliminary prototype based on 3 membrane steps to be tested at research site to overall concept assessment; b) MEDESOL-2: Full 5-steps membrane distillation system to be tested under real industrial working conditions (seawater); c) MEDESOL-3: Small stand-alone solar system to be used at isolated rural locations of developing countries; to be tested with brackish water under real working conditions. The expected result would be the development of a solar seawater desalination technology more cost-effective and efficient than other existing solar desalination processes with market possibilities in both, EU and Third Countries, thus providing sustainable development of arid and semi-arid zones.