DR, Photoionization and Opacities Nigel R. Badnell University of Strathclyde Department of Physics, Glasgow, G4 0NG, U.K. We review methodologies for describing dielectronic recombination (DR). We look briefly at the state-of-play of theory vs experiment. We then discuss how to deliver DR data in a form suitable for modelling and we review the status of the partial and total DR database being assembled for the modelling of dynamic finite-density plasmas. We comment on the role of fields and how modelling l-changing collisions approximately models the dynamic part of the plasma microfield. We also consider the inverse process of photoionization and discuss how the same approach to DR is being used for inner-shell photoionization and the determination of opacities in stellar interiors. In particular, we pay attention to the role of opacity in resolving the discrepancy between the helioseismology observations and stellar evolution models for the position of the base of the solar convective zone.