Abstract. The morphology of the Coelopidae is considered, particularly in relation to taxonomic characters, terminology, and sexual di morphism. Taxonomic relationships and family limits are discussed; the Coelopidae appear to be most closely related to the families Helcomyzidae and Dryomyzidae of the superfamily Sciomyzoidea. The following genera are excluded from the Coelopidae:ListriomastaxandApetaenus(Tethinidae),Orygma(Sepsidae),Heterocheila(orOedoparea, position doubtful). The position of the generaMalacomyia, BaeopterusandIcaridionin the Coelopidae is confirmed. The Coe lopidae are divided into two subfamilies, Lopinae subfam.n. and Coe‐lopinae. The Coelopinae include four tribes: Glumini trib.n., Coelopini, Coelopellini trib.n., Ammini trib.n. The following genera and species are described as new:Lopa, Gluma, Rhis, This, Amma, Lopa convexa, Gluma keyzeri, G.nitida, G.musgravei, Rhis whitleyi, This canus, Coe‐lopella popeae, Amma blancheae. The subgeneraFucomyiaandNeo‐coelopaof the genusCoelopaare rejected as invalid.Chaetocoelopa huttoniHarrison (1959) is a new synonym ofChaetocoelopa littoralis(Hutton, 1881).Coelopa palauensisHardy (1957) is a new synonym ofC.alluaudiSeguy (1941), which is recorded from Australia for the first time.Coelopa africanaMalloch (1933a) is a new synonym ofC.ursina(Wiedemann, 1824) from southern Africa. Keys are provided to supra‐generic groupings of Coelopidae, to the Australasian genera, and to the species ofChaetocoelopa, Coelopella, GlumaandIcaridion.Information on the biology and ecology of Coelopidae is summarized, and additional data on Australian species are recorded. Coelopids are among the most significant organisms recycling stranded kelp, because of their often enormous biomass. Their activities can be detrimental to sea‐side recreation. Parasitism byStigmatomycessp. (Ascomycetes: Laboulbeniales) is recorded for several coelopid species. The distribution patterns of coelopid taxa are