This volume belongs to the series stemming from the HERCULES Course on Neutron and Synchrotron Radiation for Condensed Matter Studies. This second volume, which corresponds to a two-week course, is devoted to selected applications in physics and chemistry of solids. This domain of applications is extremely wide and no attempt has been made to cover it entirely. The fourteen chapters range from general considerations of symmetry in condensed matter to the most recent developments in magnetic excitations and electron spectroscopies in high Tc superconductors. The subjects were chosen either for their basic importance or because of interesting new developments. The fifteen authors were selected both for their high scientific expertise and their teaching skills.