An analytical expression for static stability of a rectangular slab with two simply supported and two elastically restrained edges is presented. The linear elastic isotropic slab can represent a rigid pavement resting on an elastic foundation and loaded by a uniform in-plane axial load per unit length along the edges. The partially restrained edges are connected to the ground by translational and rotational elastic springs; an appropriate magnitude of the springs can capture classical boundary conditions such as free, simply supported, and clamped edges. Results from classical boundary conditions and a finite-element model were used to validate the proposed stability equation. The generalized boundary conditions were found to change the critical load by a factor of two and greatly affected the first buckling mode shape of a typical concrete pavement. The critical load was not sensitive to the slabβs geometry if the length was four times longer than the width, but this was not the case for small aspect ratios. Finally, the translational spring was found to be a defining factor in determining the influence of the other variables on the critical load