<p>Friction Stir Welding (FSW) is a relatively new technique to create similar and dissimilar joint of light alloys. The joint is produced under the combined effect of friction and heat by a rotating tool. The technique was developed to overcome many of the metallurgical and solidification defects that may generate during the conventional fusion welding techniques. Yet, producing a defect-free welding joint by friction stir welding requires considering of many process-related parameters. As a result of selecting unsuitable welding parameters, different types of surface and volumetric defects are formed over and inside a welding joint. These defects were proved to have an influence on the quality of the generated joint. Traditional non-destructive techniques have been used for detecting defects of FSW joints. Giving a preference to a certain non-destructive testing technique should be considered in terms of welding and material parameters including defect geometry. In addition, many friction-stir processes are employed to repair defective joints. This work spots the light on the FSW defects and the parameters that are most likely to cause them and poses the possibility of repairing some of these defects as well as the capabilities of different NDT techniques to detect FSW defects. The work was designed to be as a guide that combines between the causative parameters of FSW defects, their detection by NDT methods, and the possibility of repairing some of them as well as the possibility of predicting FSW defects using FEM software.</p>