A theoretical analysis has been undertaken for unequal width T-joints, haunch-reinforced, in square hollow structural sections (HSS). The unreinforced joint is merely a special case. The theory was based on a finite difference solution to the elastic chord flange plate equation and predicts the branch-to-chord joint stiffnesses under both bending [Formula: see text] and axial force (C = P/δ). The effects of varying the width ratio λ, overall haunch length-to-width ratio λ1, and chord width-to-thickness ratio bc/tc were studied for different plate edge boundary conditions. The latter parameter has the greatest effect on stiffness, but the other two, including haunch size, are also significant. There is reasonable agreement between the joint rotational stiffness factor J, obtained from earlier tests, and the predictions of theory for different edge boundary conditions. The unequal width, unreinforced connection is generally too weak to be viable in design applications. Haunch stiffeners improve strength and stiffness, and are particularly beneficial for large rather than small λ (i.e., 0.833 vs. 0.333).