Phosphorene is a two-dimensional material consisting of phosphorus. It consists of a single layer of the artificially made layered black phosphorus, the most stable allotrope of phosphorus. The designation phosphorene has been introduced in analogy to the designation of graphene as a single layer of graphite. Among two-dimensional materials, phosphorene emerged as a strong competitor to graphene because, in contrast to graphene, phosphorene has a nonzero fundamental band gap that can be furthermore modulated by strain and the number of layers in a stack. Phosphorene was first isolated in 2014 by mechanical exfoliation.