In recent years, there has been a major expansion of high pressure research providing unique information about systems of interest to a wide range of scientific disciplines. Since nuclear magnetic resonance has been applied to a wide spec trum of problems in chemistry, physics and biochemistry, it is not surprising to find that high pressure NMR techniques have also had many applications in these fields of science. Clearly, the high information content of NMR experiments combined with high pressure provides a powerful tool in modern chem istry. It is the aim of this monograph, in the series on NMR Basic Principles and Progress, to illustrate the wide range of prob lems which can be successfully studied by high pressure NMR. Indeed, the various contributions in this volume discuss studies of interest to physics, chemical physics, biochemistry, and chemical reaction kinetics. In many different ways, this monograph demonstrates the power of modern experimental and theoretical techniques to investigate very complex systems. The first contribution, by D. Brinkman, deals with NMR and NQR studies of superionic conductors and high-Tc supercon ductors at high pressure. Pressure effects on phase transitions, detection of new phases, and pressure effects on diffusion and spin-lattice relaxation, represent a few of the topics discussed in this contribution of particular interest to solid state physics.