This checklist comprises parts of the larger checklist of the Hymenoptera of the British Isles; the terms of reference and methodology are explained in Broad (2014). Country level distribution records, as reported here, are mainly taken from the collections of the Natural History Museum, London (NHM), with additional sources cited. The Ceraphronoidea comprises two extant families, the Ceraphronidae and Megaspilidae, represented by 28 and 64 valid species in the British Isles. Representatives of the British families and subfamilies of Ceraphronoidea are shown in Fig. 1a, c, d. There has been very little recent work on the British and Irish Ceraphronoidea and it is generally a rather neglected group of parasitoids. The genus Dendrocerus is an exception: several species are frequently reared as hyperparasitoids of aphids or from other aphid-associated insects and their taxonomy has been revised (Fergusson 1980). Much remains to be discovered about the biology and taxonomy of ceraphronoids. Whilst at least some megaspilids are known to be ectoparasitoid idiobionts (Haviland 1920), including Dendrocerus, the Ceraphronidae contains ecto- and endoparasitoids; within the same genus (Aphanogmus) some species seem to be endoparasitoids (e.g. Parnell 1963) and others ectoparasitoids (Luhman et al. 1999, Evans et al. 2005), with idiobiosis and koinobiosis both reported in the literature. Whilst hosts of both ceraphronids and megaspilids seem to be centred on Diptera there are many exceptions and the range of hosts of the superfamily spans several orders. Nomenclature here follows Johnson and Musetti (2004) a rather full synonymy is given as there is only a very small body of literature dealing with ceraphronoids in a British context, so most names are unfamiliar to most entomologists.