  Photoionization and its inverse, electron-ion recombination, are key
processes that influence many astrophysical plasmas (and gasses), and the
diagnostics that we use to analyse the plasmas. In this review we provide a
brief overview of the importance of photoionization and recombination in
astrophysics. We highlight how the data needed for spectral analyses, and the
required accuracy, varies considerably in different astrophysical environments.
We then discuss photoionization processes, highlighting resonances in their
cross-sections. Next we discuss radiative recombination, and low and high
temperature dielectronic recombination. The possible suppression of low
temperature dielectronic recombination (LTDR) and high temperature dielectronic
recombination (HTDR) due to the radiation field and high densities is
discussed. Finally we discuss a few astrophysical examples to highlight
photoionization and recombination processes.
