Friction stir welding (FSW) and friction stir spot welding (FSSW) are emergent joining technologies that are being developed for aerospace applications on a case-by-case basis to reduce part count, improve material buy-to-fly ratios, reduce cycle time, reduce lead-time requirements, lower environmental impacts, etc.  Because they are relatively new innovations, FSW and FSSW lack established industry standards and design data.  Consequently development and implementation of FSW and FSSW applications require more effort in terms of testing and verification than do developing applications utilizing conventional joining technologies (namely installed fasteners).  To help address this need, the National Institute for Aviation Research of the Wichita State University has undertaken a program to develop design properties data for joints produced in aluminum alloys by friction stir related technologies.  This program consists of two thrust areas and is based on developing friction stir technologies as local thermomechanical processing methods for forming solid state joints.  The first program is a path independence initiative for butt joints produced by friction stir welding (FSW) and is based on the observation that many aluminum alloys have been joined with a wide variety of weld tool designs.  Therefore, an unspecified number of tool designs are expected to make equally sound joints with independently developed process windows.  Any advantage one tool may have over another is expected to be evident primarily in terms of productivity, i.e. welding and processing speeds. The second program involves qualifying friction stir spot welds for lap joints as in situ integral fasteners. Individual “spots” are treated similar to conventional fasteners.  The exception is that parent material is used to form each fastener.  In both static and dynamic tests, properly designed FSSW joints are proving superior to rivets because of favorable residual stresses and the elimination of the stress concentration associated with a rivet hole.