The higher-order shear deformable plate theory presented here concerns the buckling of laminated composite plates. The theory extends Reddy's higher-order theory (1984) to include the effect of rotatory moments sometimes called curvature terms. General equations of equilibrium in terms of stress resultants and boundary conditions are derived for plates laminated of orthotropic layers. Subsequently, the equations of equilibrium and boundary conditions are also obtained in terms of kinematic variables for the special case of symmetrically laminated crossply plates.