The following results of the experimental and theoretical investigations of the spectral behavior of the photoionization cross sections in the ultrasoft X-ray region are discussed : 1. The notable depature from hydrogen-like behaviour of the atomic photoionization cross sections of the inert gases Ar, Kr and Xe ; 2. Similarity of the gross features of absorption spectra both gases and solids ; 3. Spectral behavior of absorption coefficients of Au and Bi, rare-earth metals, transition metals from Zr to Pd, and from Ti to Ni and from Ta to Au