The approximately 41-ct Dresden Green diamond is the largest, and perhaps the finest, green diamond known to have a color of natural origin. A diamond so rich in history is well worth studying for that reason alone, but the Dresden Green offers the unique opportunity of adding valuable data to the quest for means to distinguish natural from laboratory-irradiated green diamonds. In November of 1988, two senior GIA staff members visited the Green Vaults with this goal in mind. The Dresden Green diamond proved to be not only of extraordinary quality but also a very rare type IIa – one of the purest forms of diamond. In addition, the spectral characteristics of this stone were found to overlap those of k n m treated diamonds. The history locality origin, and properties of the Dresden Green diamond are discussed in detail in this article.