Stalk-eyed flies are insects of the fly family Diopsidae. The family is distinguished from most other flies by most members of the family possessing "eyestalks": projections from the sides of the head with the eyes at the end. Some fly species from other families such as Drosophilidae, Platystomatidae, Richardiidae, and Tephritidae have similar heads, but the unique character of the Diopsidae is that their antennae are located on the stalk, rather than in the middle of the head as in all other flies. Stalked eyes are present in all members of the subfamily Diopsinae, but are absent in the Centrioncinae, which retain unstalked eyes similar to those of other flies. The stalked eyes are usually sexually dimorphic, with eyestalks present but shorter in females.

The stalk-eyed flies are up to a centimeter long, and they feed on both decaying plants and animals. Their unique morphology has inspired research into how the attribute may have arisen through forces of sexual selection and natural selection. Studies of the behavior of the Diopsidae have yielded important insights into the development of sexual ornamentation, the genetic factors that maintain such a morphological feature, sexual selection, and the handicap principle.

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