This is the first book devoted to the use of X-ray beam techniques to study magnetic properties of materials. It covers both experimental and theoretical issues. The three main topics are dichroism, elastic scattering (both non-resonant and resonant diffraction) and spectroscopy. In the past decade there has been an expansion of activity in the field, driven by the availability of intense, tuneable and highly polarized X-ray beams from synchrtron facilities. The pace of events is likely to continue with the start of new (3rd generation) facilities, including the European Synchrotron Radiation Facility, Grenoble, and the Advanced Light Source, Argonne National Laboratory. USA.