In this thesis, experimental and mathematical investigations on single and double effect desalination systems are reported. The yields of solar still were in the range of 2-4 lit/(m2.day) according to the type of still and the location /season in which it was reported. To increase the efficiency of desalination system one must attempt to reuse latent heat of vaporization which in simple solar still is wasted and increasing temperature difference. This leads of multi-effect solar stills. The system comprises from two parts, the heating section which resembles a solar collector that heats up the heat transfer fluid at the desired rate. The heat input is then naturally convected to the desalination part which is a multi-effect evaporation-condensation unit. Heat is transferred from the hot fluid to saline water and makes it to evaporate. Water vapor is then condensed on the next effect where heat of condensation of water acts as heat input to the next effect. The total yield for the single effect showed 94% increase with respect to a conventional solar still (increasing water temperature). The total yield for the double effect showed 70% increase with respect to a single effect solar still (heat recovery). The effects of some parameters such as water depth, input radiation intensity ,and increase in salinity reduces the system production rate increasing the power input from 200 to 500 W/m2 (That is 150% increase) results in 236%, 240% increasing in the production rate of single and double effect respectively. In the present work the depth of water in the first effect was changed from 1 to 3cm while water depth in second effect of double effect was kept constant at 1cm. increasing the water depth from 1 to 3cm results in 14%, 26% decreases in the production rate of single and double effect respectively. The daily production decreases as the salt concentration increases. Increase in the water salinity from 0% to 3.5% results in 20% decreases in the daily production.