The article discusses diamonds and their high-pressure, high-temperature (HPHT) processing. Topics include the HPHT processes, namely, HPHT treatment and HPHT diamond growth, the launching by General Electric Co. (GE) and Lazare Kaplan International of the first commercial HPHT-treated color diamonds in March 1999, and the processing of large green and yellow diamonds colored by nickel impurities.