Friction Stir Welding (FSW) was invented by Wayne Thomas at TWI (The Welding Institute), and the first patent applications were filed in the UK in December 1991. Initially, the process was regarded as a “laboratory” curiosity, but it soon became clear that FSW offers numerous benefits in the fabrication of aluminum products. Friction Stir Welding (FSW) has become a major joining process in the aerospace, railway and shipbuilding industries especially in the fabrication of aluminum alloys. The process uses a spinning non-consumable tool to generate frictional heat in the workpiece. Worldwide, there are now over 135 licensees of FSW and new techniques and applications are being developed daily. This paper looks at the review, on friction stir welding process, various welding variables like tool rotation, transverse speed, tool tilt, plunge depth and tool design, for the welding of aluminum alloys or various dissimilar alloys. Applications, future aspects, and several key problems are also described.