Ballistic limit curves are determined by using experimental and theoretical results for the permanent deformation of a plate subjected to an impact load. The experiments have been performed on shielded plates of various thicknesses and materials at the Hypervelocity Impact Research Laboratory of NASA JSC. Comparison of the theoretical and experimental deformations allows one to determine the dynamic yield strength of the plate material. It is assumed that the shields can be replaced by a single equivalent shield, and that the debris cloud produced by the impact expands according to the theory of Swift. A strain criterion is imposed and ballistic limit equations describing the critical projectile radius and the critical backwall thickness are derived. The corresponding curves are plotted for the case of the most damaging impact conditions. Comparison is made with empirical limit curves that are available in the literature.