The book gives insight to butt joining of AISI 316L stainless steel of 3 mm thick by FSW process (from first attempt to a successful weld).The preliminary experimental trials were carried out to identify a potential FSW tool material.Three tungsten based FSW tools were identified and a detailed experimental analysis was performed. The weld quality & weld integrity was accessed by x-ray radiography test & SEM analysis, whereas, the performance of FSW tools was measured by photographic and mass loss techniques. The working range for each process parameters was found and a working window was developed. The optimal process parameters for the maximization of the response, ultimate tensile strength was found using non- linear optimization method. The mechanical and microstructural properties of the weld joints were explored to correlate structure - property relations. Advanced characterization techniques such as XRD,TEM and EBSD were used for in-depth microstructural analysis. Pitting corrosion behaviour of the FSW joints was evaluated using cyclic polarization technique. Underwater FSW was performed in a 3.5 NaCl cooling medium to compare the properties to that of normal FSW Joints.