A dragonfly is an insect belonging to the order Ordonata, the suborder Epiprocta or, in the strict sense, the infraorder Anisoptera. It is characterized by large multifaceted eyes, two pairs of strong transparent wings, and an elongated body.

 Dragonflies typically eat mosquitoes, midges and other small insects like flies, bees, and butterflies. They are usually found around lakes, ponds, streams, and wetlands because their larvae, known as "nymphs", are aquatic.

Dragonflies do not normally bite or sting humans (though they will bite in order to escape, for example, if grasped by the abdomen); in fact, they are valued as a predator that helps control the populations of harmful insects, such as mosquitoes. It is because of this that dragonflies are sometimes called "mosquito hawks" in North America along with the Crane Fly (which, in fact, does not eat mosquitoes).

In Europe, dragonflies have often been viewed as sinister. Some English vernacular names, such as "devil's needle" and "ear cutter", link them with evil or injury. A Romanian folk tale says that the dragonfly was once a horse possessed by the devil, and Swedish folklore holds that the devil uses dragonflies to weigh people's souls. Another Swedish legend holds that trolls use the dragonflies as spindles when weaving their clothes (hence the Swedish word for dragonfly trollslända, lit. "troll's spindle") as well as sending them to poke out the eyes of their enemies. The Norwegian name for dragonflies is "Øyenstikker", which literally means Eye Poker. They are often associated with snakes, as in the Welsh name gwas-y-neidr, "adder's servant". The Southern United States term "snake doctor" refers to a folk belief that dragonflies follow snakes around and stitch them back together if they are injured. The Lithuanian word "Laumzigis" is a composite word meaning "the Lauma's horse", while in Dutch, Aeshna mixta is called "Paardebijter" or "horse biter". In some South American countries, dragonflies are also called matacaballo (horse killer), or caballito del diablo (devil's horse), since they were perceived as harmful, some species being quite large for an insect.

In East Asia and among Native Americans, dragonflies have a far better reputation, one that can also be said to have positively influenced modern day views about dragonflies in most countries.

For some Native American tribes they represent swiftness and activity, and for the Navajo they symbolize pure water. Dragonflies are a common motif in Zuni pottery; stylized as a double-barred cross, they appear in Hopi rock art and on Pueblo necklaces.  It is said in some Native American beliefs that dragonflies are a symbol of renewal after a time of great hardship.

In Japan dragonflies are symbols of courage, strength, and happiness, and they often appear in art and literature, especially haiku. In ancient mythology, Japan was known as Akitsushima, which means "Land of the Dragonflies". The love for dragonflies is reflected by the fact that there are traditional names for almost all of the 200 species of dragonflies found in and around Japan. Japanese children catch large dragonflies as a game, using a hair with a small pebble tied to each end, which they throw into the air. The dragonfly mistakes the pebbles for prey, gets tangled in the hair, and is dragged to the ground by the weight.

They also have traditional uses as medicine in Japan and China. In some parts of the world they are a food source, eaten either as adults or larvae; in Indonesia, for example, they are caught on poles made sticky with birdlime, then fried in oil as a delicacy.