This text provides an up-to-date coverage of the theoretical and experimental tools required for fundamental studies of point defects, with illustrative examples from a wide range of inorganic materials. On the experimental side a strong emphasis is placed on the powerful resonance and hyperfine methods which give detailed information on defect structures. Theoretical chapters cover statistical and quantum mechanical methods, particularly the computer simulations techniques which are now widely employed. The examples of applications of defect properties highlight the benefits of a controlled inclusion of defect properties for modern advanced technologies. This work provides coverage of the theoretical tools required for defect study, putting strong emphasis on the wide range of experimental techniques needed for analysis. Particular attention has been given to the powerful resonance and hyperfine methods which often give more detailed data than classical methods.