X-ray spectroscopy of astrophysical plasmas.

We provide a qualitative review of key X-ray spectral diagnostics of astrophysical plasmas. We begin with a brief discussion of the two major types of equilibria, collisional ionization and photoionization, and then consider the behaviour of hydrogen-like, helium-like, iron L-shell and iron K-shell transitions for these separate cases. Where possible, we discuss explicit examples using high-resolution spectra acquired by the grating instruments on the Chandra and XMM-Newton observatories.