Nymphalis antiopa, known as the Mourning Cloak in North America and the Camberwell Beauty in Britain, is a large butterfly native to Eurasia and North America. See also Anglewing butterflies.

The immature form of this species is sometimes known as the spiny elm caterpillar. Other older names for this species include Grand Surprise and White Petticoat. A powerful flier, this species is sometimes found in areas far from its usual range during migration.

These butterflies have a life-span of 11 to 12 months, one of the most extensive life-spans for any butterfly.

It is also the State Insect of Montana, adopted in 2001.