Friction Stir Welding (FSW) is a new and innovative solid state joining process that now allows the welding of previously unweldable aluminum alloys. Traditionally, these alloys have found use only in mechanically joined structures. Discussed is an overview of the FSW process for both full penetration butt welds and partial penetration lap welds, as well as the specific metallurgical and mechanical properties of friction stir welded lap shear joints in 2090-T83 aluminum lithium alloy. Flat sheet shear testing of friction stir welded and riveted specimens are compared, as are compression buckling tests of stringer stiffened panels. The results of these studies indicate that friction stir welding is a viable and potentially cost reducing alternative to aluminum riveted structures.