Psilocybe cyanescens, commonly known as the wavy cap or potent psilocybe, is a species of potent psychedelic mushroom. The main compounds responsible for its psychedelic effects are psilocybin and psilocin. It belongs to the family Hymenogastraceae. A formal description of the species was published by Elsie Wakefield in 1946 in the Transactions of the British Mycological Society, based on a specimen she had recently collected at Kew Gardens. She had begun collecting the species as early as 1910. The mushroom is not generally regarded as being physically dangerous to adults. Since all the psychoactive compounds in P. cyanescens are water-soluble, the fruiting bodies can be rendered non-psychoactive through parboiling, allowing their culinary use. However, since most people find them overly bitter and they are too small to have great nutritive value, this is not frequently done.

Psilocybe is a genus of gilled mushrooms, growing worldwide, in the family Hymenogastraceae. Many species contain the psychedelic compounds psilocybin and psilocin.