Odonata is an order of insects, encompassing dragonflies (Anisoptera) and damselflies (Zygoptera). The word dragonfly is also sometimes used to refer to all Odonata. The term odonate has been coined to provide an English name for the group as a whole, but is not in common usage; most Odonata enthusiasts avoid ambiguity by using the term true dragonfly, or simply Anisoptera, when referring to just the Anisoptera.

The largest living odonates are the giant Central American damselfly Megaloprepus coerulatus, and the Giant Hawaiian Darner (Anax strenuus), a dragonfly endemic to the Hawaiian Islands. The prehistoric "giant dragonflies" belonged to the Protodonata (or Meganisoptera), closely related to true dragonflies but not part of the Odonata in the restricted sense.

Lestes dryas is a species of damselfly which is found across Europe, Asia and North America. In North America it is known as the Emerald Spreadwing and this name is becoming more widely used in Europe. In Britain, it is very rare, and its popular name is the Scarce Emerald Damselfly. It can tolerate extreme conditions that few other dragonflies can survive.