Since its first isolation by Hennig Brand in 1669, the elemental phosphorus is found to show more allotropic modifications than any other element. 1, 2 At ambient condition, well-known stable phosphorus phases include white, red, and black allotropes (Table 3.1). At nonambient condition, more allotropes like crystalline violet, red, brown, and gray can be synthesized. In particular, a scarlet phase can be formed under x-ray radiation of white phosphorus. With a valence configuration of 3s23p x 3p y 3p z , phosphorus allows twofold, threefold, and fourfold coordinated neighbors, which accounts for its large number of polyphosphides. In the following sections, the introduction of the common phases of phosphorus is given.