In the last few years a surprisingly large number of new experimental techniques have been devised to probe, often with great subtlety, into the electronic structures of inorganic substances. Thus in favourable cases one now has the opportunity of locating and assigning electronically excited states over a 1 vast energy range stretching from tens of cm- above the ground 1 6 state up to some 10 cm- • The techniques are extremely dis­ parate in background, involving (among others) linearly and circularly polarised electromagnetic radiation, electron kinetic energy analysis and neutron scattering. Furthermore, practition­ ers of many of the techniques may not be aware of how the information which they are obtaining overlaps and complements that obtained by other techniques. The time therefore seemed ripe to bring together a group of experts to survey, for an audience of inorganic chemists, the basic theories and experim­ ental procedures relevant to the different techniques, and the relations between them. In pursuing this aim we were fortunate in having the very generous financial backing of N. A. T. O. , through their Advanced Study Institutes programme, and the present volume records the substance of lectures given at the Institute which took place at the Inorganic Chemistry Laboratory and St. John's College, Oxford, from 8-18 September 1974.