High-temperature and high-pressure treatment of diamond is becoming an important technology to elaborate diamonds. This is the first book providing a comprehensive review of the properties of HPHT-treated diamonds, based on the analysis of published data and the work of the authors. The book gives a detailed analysis of the physics of transformation of internal structures of diamonds subjected to HPHT treatment and discusses how these transformations can be detected using methods of optical microscopy and spectroscopy. It also gives practical recommendations for the recognition of HPHT-treated diamonds. The book is written in a language and terms which can be understood by a broad audience of physicists, mineralogists and gemologists.