Modern technology depends on materials with precisely controlled properties. Ion beams are a favoured method to achieve controlled modification of surface and near-surface regions. In every integrated circuit production line, for example, there are ion implantation systems. In addition to integrated circuit technology, ion beams are used to modify the mechanical, tribological and chemical properties of metal, intermetallic and ceramic materials without altering their bulk properties. Ion-solid interactions are the foundation that underlies the broad application of ion beams to the modification of materials. This text is designed to cover the fundamentals and applications of ion-solid interactions and is aimed at graduate students and researchers interested in electronic devices, surface engineering, reactor and nuclear engineering and material science issues associated with metastable phase synthesis.