Book excerpt: Opacity is a quantity that determines the transport of radiation through matter and is important in many problems in physics and astrophysics. To calculate opacities, one requires atomic data for a large number of processes involving the absorption and scattering of radiation. Stellar opacities are of particular interest in astrophysics because of their importance for theories of stellar structure and stellar pulsations. Taking advantage of advances in computational atomic and plasma physics and of the availability of powerful supercomputers, The Opacity Project, Volume 2: Selected Research Papers-Atomic Data Tables for S to Fe presents accurate atomic data required for opacity calculations. The work includes computation of energy levels, oscillator strengths, photoionization cross sections, and parameters for pressure broadening of spectral lines. The book uses several different methods of computation to calculate the same data, thereby providing a check on the validity of the data. Divided into two parts, the first presents seven key research papers that review available data and detail the relevant atomic data calculations while the second part provides tables of energy levels and oscillator strengths for the elements S, Ar, Ca and Fe. The Opacity Project Team is comprised of 30 experts from 13 leading international laboratories and observatories in atomic physics and astrophysics.