This publication is concerned with the characterization of materials for industries in general and the nuclear energy sector in particular. The main focus is on research reactor based techniques, with some discussion of other related methods, such as positron annihilation. Demand for energy is rising with the increase in industrial development worldwide. Nuclear fission and fusion are seen as important future energy sources. Development of innovative reactor designs with high efficiency for fuel burnup is one of the challenges for fission. Materials resistant to high doses of radiation pose a major challenge for fusion. In both cases, the development of well characterized, high quality materials is essential for the safe, efficient and reliable operation of engineering components.