Onchidiidae are a family of small, air-breathing sea (and land) slugs. They are shell-less marine (except for two species) pulmonate gastropod molluscs. Onchidiidae is the only family within the superfamily Onchidioidea.

These animals are quite unusual in that they are emphatically not opisthobranchs with gills, as are almost all of the sea slugs. Instead these creatures are pulmonates. They are more closely related to air-breathing land and freshwater snails and slugs than they are to most other sea snails and sea slugs.

This family has no subfamilies (according to the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005).

143 species names were created within the Onchidiidae, but until recently few species could be identified. In the late 1920s Hoffmann revised the family (based on the descriptions), and classified the described species into genera. Labbé later continued the revision and named many new genera in his classification of onchidiid slugs. Labbé also made mistakes in describing the anatomy of some species, and the Onchidiidae was not revised again for over 80 years. The genus Onchidium was revised in 2016 based on natural history, comparative anatomy, and DNA sequences. This was followed by revisions of the other onchidiid genera, and the descriptions of onchidiid species in several new genera.

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