ESDU 80023 defines the specially-orthotropic plate. Buckling loads are presented in terms of the plate geometry and the four flexural stiffnesses for a variety of edge conditions for plates loaded in uniaxial or biaxial compression, shear and shear with uniaxial compression. The analysis assumes the through-thickness shear stiffness is sufficiently large for the bending stiffnesses to control buckling. A criterion is given to check whether that is so and, if it is not met, the program of ESDU 81047 or ESDU 94005 (ESDUpac A8147 or ESDUpac A9405) should be used; those programs include the effect of shear stiffness.