Electron or positron storage rings are the most powerful sources of ul
traviolet and X-ray photons available to experimentalists interested i
n spectroscopic and structural studies in condensed matter. The most r
ecent generation of synchrotron radiation sources is characterized by
an increase by several orders of magnitude in brilliance. The potentia
lities opened up by these new machines are illustrated by the results
of recent experiments at ESRF in Grenoble.