Friction stir welding (FSW) is a new solid state connection process for soft materials such as aluminium and magnesium alloys because it avoids many of the common problems associated with fusion welding.In this process, a cylindrical-shouldered tool with a profiled probe is turned at a constant speed and fed at a constant traverse rate into the joint line between two pieces of plate material, which are butted together. The weld quality and cost is mainly dominated by selection of appropriate process parameters in friction stir welding technique.FSW has many welding parameters such as tool rotation speed, welding speed, tool tilt angle, tool material, pin profile and shoulder diameter. Here we review and critically examine several important aspects of process parameters on friction stir welding of magnesium alloy.