The paper is devoted to experimental and theoretical studies of ablation of condensed matter by optical (OL), extreme ultraviolet (EUV) and X-ray lasers (XRL). Results obtained at two different XRL are compared. The first XRL is collision Ag-plasma laser with pulse duration τL = 7 ps and energy of quanta hv =89.3 eV, while the second one is EUV free electron laser (EUV-FEL) and has parameters τL = 0.3 ps and energy of quanta 20.2 eV. It is shown that ablation thresholds for these XRL at LiF dielectric are approximately the same. A theory is presented which explains slow growth of ablated mass with fluence in case of XRL as a result of transition from spallative ablation near threshold to evaporative ablation at high fluencies. It is found that the metal irradiated by short pulse of OL remains in elastic state even in high shear stresses. Material strength of aluminum at very high deformation rates V/V ~ 109 s-1 is defined.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.