The approximate theory of internal buckling of multilayers is obtained by a direct method and generalized to nonsinusoidal deformations. The numerical discussion includes the case of unequal thickness of competent and incompetent layers. Simple expressions are derived for the dominant wave length for rigid confinement or self-confinement showing the influence of interstitial flow. The theory is presented in the context of viscous media using both solid and fluid mechanics and is valid for large compressive strain and moderate slopes. Its applicability to elastic and viscoelastic media is indicated.