Gall wasps, also traditionally called gallflies, are hymenopterans of the family Cynipidae in the wasp superfamily Cynipoidea. Their common name comes from the galls they induce on plants for larval development. About 1,300 species of this generally very small creature are known worldwide, with about 360 species of 36 different genera in Europe and some 800 species in North America.

The Cynipoidea are a moderate-sized hymenopteran superfamily that presently includes seven extant families and three extinct families, though others have been recognized in the past. The most familiar members of the group are phytophagous, especially as gall-formers, though the actual majority of included species are parasitoids or hyperparasitoids. They are typically glossy, dark, smooth wasps with somewhat compressed bodies and somewhat reduced wing venation. It is common for various metasomal segments to be fused in various ways, and the petiole is very short, when present.