Gasteruption is an easily recognized genus of wasps whose larvae are predator-inquilines in the nests of cavity-nesting solitary bees (Apidae, Colletidae, Halictidae and Megachilidae), with some records for solitary wasps as hosts (Crabronidae, Vespidae and Sphecidae). There is conflicting information about the biology and host associations for the genus because of a lack of information from the majority of biogeographical regions in the world. Here we concatenate all available literature records pertaining to the biology of adults, host associations and larval development. We conclude that bee hosts are more readily used compared to wasp hosts (71 bee, 13 wasp species), with the majority of wasp observations without sufficient data to be confident of the host association. The majority of known records are for hosts nesting in cavity nests (76 species) rather than ground nests (eight species), with most species recorded from a single host association. From available data, the approximate rates of host nests with parasitized broods are low: 4–7%. We also provide suggestions for improving the quality of future observations in the group.