``Spectroscopy of Crystals Containing Rare Earth Ions'' contains chapters on some key problems selected from a broad range of spectroscopic studies of RE-activated solids including both crystalline and glassy materials. Progress in crystal field theory is surveyed, an area which is basic to our understanding of the energy levels. The treatment of dynamical properties includes studies of coherence phenomena in isolated ions, energy transfer between ions and co-operative phenomena associated with ion-ion and ion-lattice interactions. In addition, the role of electron spins and nuclear spins is studied by light scattering and double resonance techniques. The presence of inhomogeneous broadening of spectral lines is observed and studied in many contexts, leading to new insights into general problems of the disordered state. Considerable attention is devoted to describing new experimental techniques whose development is of prime importance for progress in the spectroscopy of RE-activated solids. Many of these rely on the development and application of tunable lasers. At the moment this is a very active field of spectroscopy with more exciting developments likely to occur in the future.