Theridiosomatidae, commonly known as ray spiders, are a family of araneomorph spiders first described by Eugène Simon in 1881. The family includes more than 100 species divided between 23 genera.

Ray spiders are small arachnids, usually less than 3 mm in body length, best known for their distinctive cone-shaped webs and their remarkable hunting technique of using their webs as high-speed slingshots to capture prey.

The family name Theridiosomatidae is derived from the type genus Theridiosoma, which was established by Octavius Pickard-Cambridge in 1879.

Ray spiders are chiefly cosmotropical in distribution. Around half the genera are restricted to the Neotropics, while most other genera occur in the Old World Tropics. A few genera are present in both.

Few species reach the cold temperate regions (T. gemmosum in Europe and North America, T. epeiroides in Korea and Japan). Theridiosomatids are apparently absent from western North America. The monotypic genus Parogulnius may be misplaced in this family.

Theridiosomatids live almost exclusively in wet or humid, shaded forest habitats. Plato is troglophilic, and Theridiosoma also is common around cave entrances. All species seem to prefer dark situations. Webs typically occur near ground in low vegetation or leaf litter.

Ray spiders are small ecribellate, colulate, entelegyne spiders of the superfamily Araneoidea. Total length ranges from 0.5 to 3.0 mm, usually less than 2.5 mm.

The spiders have eight subequal eyes arranged in two rows, with laterals juxtaposed. The clypeus height is variable, usually more than half an anterior median eye diameter. The carapace is glabrous or with few scattered bristles, pear-shaped, with length and width subequal. The cephalic region is frequently elevated.