A comprehensive review is presented on opacity and equation of state calculations for gases, plasmas, and grains.  The continuous trasnformation of the equilibrium composition of these phases of matter as a function of temperature and density is emphasized.  Absorption and scattering processes are described that affect opacities in regions of interest to science and technology, up to temperatures of about 1 x 10(9) (o) K and densities of about 10(9) g cm (-3).  Reliability of results based on various approximations are given and cross sections are compared with experimental values where available.  Opacity tables are presented for air, "glass", a few elements, and astrophysical mixtures.weiterlesen