Technical Abstract: The genus Prunus, of the family Rosaceae, encompasses the species commonly referred to as the stone fruits, because the seed is protected by a hard pit or endocarp. The most important stone fruits are almond, apricot, sweet and sour cherry, peach and nectarine, and European and Japanese plums. Rehder divided Prunus into five subgenera: Prunophora (plums and apricots), Amygdalus (peaches, nectarines and almonds), Cerasus (cherries), Padus racemose or bird cherries) and Laurocerasus (laurel cherries). C. Ingram added a sixth sub-genus, Lithocerasus by splitting out the bush and rock cherries. While these sub-genera are convenient, some of the minor species do not fit as neatly into the groups as one might like. In addition to the crops themselves, numerous related species are found throughout the temperate regions of the world. In fact, all the Prunus are native to the northern hemisphere except for the distantly related laurel cherries in Africa and south Asia (formerly Pygeum sp.) and capuli, the spread of which to South America may have been by humans. Many of these minor species once were, and in some cases still are, used for human consumption. Often these species are grown in areas where the climate limits production of the more popular commercial crops. For most of the commercial fruit crops in their regions of origin and diversity, there are feral trees or wild relatives. Sometimes these relatives or forms are used as rootstocks, such as wild mazzard (P. avium) or the wild peach, P. davidiana. This chapter briefly mentions some of the other cultivated Prunus that do not fit neatly into a related crop discussion.