Amanita muscaria, commonly known as the Fly Agaric, is a poisonous and psychoactive basidiomycete fungus, one of many in the genus Amanita. Native throughout the temperate and boreal regions of the Northern Hemisphere, Amanita muscaria has been unintentionally introduced to many countries in the Southern Hemisphere, generally as a symbiont with pine plantations, and is now a true cosmopolitan species.

It associates with various deciduous and coniferous trees. The quintessential toadstool, it is a large white-gilled, white-spotted, usually deep red mushroom, one of the most recognizable and widely encountered in popular culture.

Several subspecies, with differing cap colour, have been recognised to date, including the brown regalis (considered a separate species), the yellow-orange flavivolvata, guessowii, and formosa, and the pinkish persicina.