The Phasmatodea are an order of insects whose members are variously known as stick insects, stick-bugs, walkingsticks, stick animals, or bug sticks. They are also occasionally referred to as Devil's darning needles, although this name is shared by both dragonflies and crane flies. They can be generally referred to as phasmatodeans, phasmids, or ghost insects, with phasmids in the family Phylliidae called leaf insects, leaf-bugs, walking leaves, or bug leaves. The group's name is derived from the Ancient Greek φάσμα phasma, meaning an apparition or phantom, referring to their resemblance to vegetation while in fact being animals. Their natural camouflage makes them difficult for predators to detect; still, many species have one of several secondary lines of defense in the form of startle displays, spines or toxic secretions. Stick insects from the genera Phryganistria, Ctenomorpha, and Phobaeticus include the world's longest insects.

The family Phylliidae contains the extant true leaf insects or walking leaves, which include some of the most remarkably camouflaged leaf mimics (mimesis) in the entire animal kingdom. They occur from South Asia through Southeast Asia to Australia. Earlier sources treat Phylliidae as a much larger taxon, containing genera in what are presently considered to be several different families.