This research study the two main technologies of seawater desalination: Thermal and Membrane Technologies. Thermal technology contained; Multi-Stage Flash distillation which is the common thermal process, Multiple Effect Distillation (MED) and Vapour Compression Distillation (VC). Membrane Technologies, It has been touched to two technologies with specific details, Reverse Osmosis (RO) and Electrodialysis (ED). The research contain a practical parts, such as: a design of Reverse Osmosis Plant & Evaluation of the Electrodialysis process.