The American Ermine (Mustela richardsonii), also known as the American stoat, short-tailed weasel, or simply as stoat, or ermine, is a species of mustelid native to most of North America.
It is a member of the genus Mustela of the family Mustelidae, distinguished from the least weasel by its larger size and longer tail with a prominent black tip. Once considered to be the same species as the Eurasian ermine (M. erminea), the American ermine was recognized as distinct in 2021, along with the Haida ermine (M. haidarum).