Friction Stir Welding (FSW) is a new, environmental friendly and energy saving solid phase joining technology that has gained keen focus of research in the welding field. This article provides a comprehensive insight on basic principle of FSW, the process parameters of FSW, and tool design. It also covers weldability, property enhancement, and a review of potential advantages and applications of the process. Joining of alloys could be a major problem in many sectors that include automotive, aerospace, ship building industries, and so on; where fusion welding is not possible due to large difference in physical and chemical properties of the components to be joined. FSW can solve such problems as it can join different alloys of aluminium and also of hard materials like steels because it avoids the common problems obtained in conventional welding processes. Common welding defects arise during welding of dissimilar materials such as porosity, solidification cracking and chemical reactions. It can be avoided with optimized FSW provided special attention is paid to the process parameters, tool design and joint design.