A potential fault causing condition in Friction Stir Welding (FSW) is misalignment, when the FSW tool is off-track from the weld line.  In this research, we present a means for automatically detecting misalignment and correcting it using a technology called “Through the Tool Tracking” (patent pending).     Force sensors attached to the tool detect signals which are then processed to discern the location of the tool relative to the weld line.  The system then adjusts the location to maintain proper tracking.    This technique is demonstrated on T-Joint FSW, in which the actual weld line is not visually observable, and yet is detectable to the system.  This demonstrates the ability to track weld lines in real time in FSW.  The paper also discusses the application of this technique to other FSW types, such as butt and lap welds.