A comprehensive treatment of the taxonomy and geographical distribution of the Euchaetidae, a typically carnivorous marine Calanoid family with a worldwide distribution in the whole depth range. The author redefines the family and its two genera. Species groups recognized in each genus and a total of 75 species found are described in detail and illustrated with figures. Geographical range is determined for most of the species. Keys are presented for identification of the species groups and the species in each group.