Historically, the first observation of a relativistic effect in atomic spectra was probably the discovery by Fraunhofer of the splitting of the Nai doublet in the solar spectrum. Thus theoretical understanding of these effects has long been important for interpreting astrophysical spectra, and it is especially important for the ultraviolet and X-ray spectra which form our subject today, for these often arise in highly ionized atoms. Because the relative importance of relativistic to non-relativistic terms is proportional to Z2, where Z is the nuclear charge, relativistic effects often play a major role in such atoms.