The eastern gray squirrel (Sciurus carolinensis), known outside of the United States as the grey squirrel, is a species of tree squirrel in the genus Sciurus. It is native to eastern North America, where it is the most prodigious and ecologically essential natural forest regenerator.[6][7] Widely introduced to certain places around the world, the eastern gray squirrel in Europe, in particular, is regarded as an invasive species. In Europe, Sciurus carolinensis is included (since 2016) in the list of Invasive Alien Species of Union concern (the Union list).[8] This implies that this species cannot be imported, bred, transported, commercialized, or intentionally released into the environment in the whole of the European Union.[9]