The underlying theoretical aspects of X-ray spectroscopies are recapitulated with special emphasis on applications to magnetic systems. Prominence is placed on common conceptual aspects, while highlighting the differences in information that they may offer. X-ray scattering can be used to investigate the electronic and magnetic long-range order in crystals and ordered materials. The crystal symmetry of the sample and the X-ray polarization state have a profound effect on the scattering amplitude of X-ray resonant magnetic scattering (XRMS). Expressions for X-ray magnetic circular and linear dichroism (XMCD and XMLD, respectively) can be derived directly from those for XRMS. The photon–matter interaction for electric and magnetic multipole fields is presented from a general point of view, which reveals the physical implications of the various terms in the cross section for X-ray absorption. X-ray optical activity is due to mixed terms of different multipole rank of the electric and magnetic fields. The different optical effects, such as XMCD, X-ray natural circular dichroism (XNCD) and X-ray magnetic chiral dichroism (XMχD), can be distinguished by their properties under space inversion and time reversal.