In this study, two-dimensional (plane-stress and plane-strain) theoretical models are presented for the stress analysis of adhesively bonded single-lap composite joints subjected to thermal, mechanical loads and a combination thereof. The joints consist of similar/dissimilar orthotropic or isotropic adherends and an isotropic adhesive interlayer. The governing diffierential equations of the problem are obtained using a variational method which minimizes the complementary strain energy in the bonded assembly. In this formulation, through-thickness variation of shear and peel stresses in the interlayer is considered. All the traction free boundary conditions are exactly satisfied. Peel and shear stresses obtained from plane-strain analytical models considering mono-modulus adhesive interlayer are in good agreement with the finite element predictions. A systematic parametric study is conducted to identify an ideal set of geometrical and material properties for the optimal design of joints.