Accelerator based methods using ion beams form a valuable set of techniques for characterising, modifying and developing materials which complement and extend the technological uses of other energy beam methods involving lasers, synchrotron sources, neutrons and electron beams. Such methods, many first developed and increasingly used in the nuclear industry over the last decade, are currently being rapidly exploited in other high technology areas in the chemical, micro-electronics and biotechnology industries. These methods are based on the inherent atomic and nuclear properties of fast ion beams in materials; ions slow down and stop by atomic collision within well-defined depths which depend on the energy and species. By the suitable choice of these parameters, the depth of interaction can be precisely controlled over a very wide range from nanometres to centimetres, which covers the range of depths which exhibit material surface properties such as corrosion, oxidation, wear and catalysis. Nuclear interactions during the slowing down process produce primary and secondary radiations with predictable strength so that concentrations of the element isotopes can be determined. Microstructural and microanalytical information can often be obtained non-destructively and sometimes on-line to the working environment.