This study uses published and unpublished data to create a comprehensive and up-to-date synthesis of available information on a little-known group of invertebrates, namely, non-marine giant ostracods (cypridids ≥3 mm long). Approximately 8% of the ∼1000 living cypridid species are identified as ‘giant’. They occur in a range of subfamilies, in all zoogeographic regions, except Antarctica, and mainly in small standing-water ecosystems. Only those in the subfamily Mytilocypridinae are reasonably well studied. This subfamily is endemic to Australia and comprises a diverse range of giant species (∼29 species in 6 genera), mainly in temporary habitats, mostly salt lakes, including in extreme conditions. We evaluate the current taxonomy of the Mytilocypridinae, analyse patterns in the field distributions and abiotic tolerances of species, and review the general biology of these ostracods. We also identify those species most in need of consideration in conservation planning, highlight critical gaps in knowledge and show how these ostracods could serve as useful models for testing ecological and evolutionary theories. The results of this study can be used to inform conservation planning for giant ostracods and direct further study of these unique invertebrates, which are an important component of the biodiversity of small standing-water ecosystems.