The observation of magnetic effects in X-ray scattering dates from the second decade of the twentieth century, before becoming associated with gamma ray phenomena in the quest to understand neutrino helicity, some thirty years later. The paradigm-changing studies in both realms of coherent and incoherent magnetic scattering also predate the availability of synchrotron radiation, which crucially possesses the polarization properties that make it a potent probe of magnetization. This review will cover the historical development, summarize the underlying interpretive theory and conclude with an example of recent research on rare earth compounds. (C) 2007 Elsevier B.V. All rights reserved