Extended shear tab connections are widely used to connect beams to the webs of girders. In the full-depth configuration of extended beam-to-girder shear tabs, the shear plate is typically fillet welded to the web, as well as to the top and bottom flanges of the girder. Due to the extended nature of the shear tab, i.e. the connection to the beam is actually made well outside of the cross-section of the girder, the inelastic stability of this plate must be accounted for in design. A coordinated experimental and numerical investigation of the behaviour and stability requirements of full-depth extended shear tabs is described in the paper. The findings from a detailed finite element (FE) simulation of 3 single-sided beam-to-girder shear tab connections, tested at McGill University, are discussed. Based on the FE analyses, the load transfer mechanism and the buckling capacity of the stiffened portion of the full-depth shear tab were determined. The parameters, which influenced the buckling of the stiffener, were studied; including the depth and thickness of the shear plate, the depth of the girder, the width of the girder flanges, and the flexibility of the girder web. Further FE analyses were completed to determine the buckling capacity of the shear tab with reduced depth of the stiffener. In addition, the load-transfer mechanism and buckling capacity of these shear plates were modeled when they are used in double-sided configurations, i.e. when a beam is placed on both sides of the girder.