The Mymaridae, commonly known as fairyflies or fairy wasps, are a family of chalcidoid wasps found in temperate and tropical regions throughout the world. The family contains around 100 genera with 1,400 species.

Fairyflies are very tiny insects, like most chalcidoid wasps, mostly ranging from 0.5 to 1.0 mm (0.020 to 0.039 in) long. They include the world's smallest known insect, with a body length of only 0.139 mm (0.0055 in), and the smallest known flying insect, only 0.15 mm (0.0059 in) long. They usually have nonmetallic black, brown, or yellow bodies. The antennae of the females are distinctively tipped by club-like segments, while male antennae are thread-like. Their wings are usually slender and possess long bristles, giving them a hairy or feathery appearance, although some species may have greatly reduced stubby wings or lack wings altogether. They can be distinguished from other chalcidoids by the H-shaped pattern of sutures on the front of their heads.

Fairyflies are among the most common chalcidoids, but are rarely noticed by humans because of their extremely small sizes. Their adult lifespans are very short, usually only a few days. All known fairyflies are parasitoids of the eggs of other insects, and several species have been successfully used as biological pest control agents.

The fossil record of fairyflies extends from at least the Albian age (about 107 myr) of the Early Cretaceous.