Lampreys are jawless fishes (Cyclostomata) that are distributed antitropically around the world. Of the three extant lamprey clades (Petromyzontidae, Geotriidae, and Mordaciidae), Geotriidae and Mordaciidae are only found in the Southern Hemisphere. Geotriidae includes two anadromous species, G. australis and G. macrostoma, while Mordaciidae includes three species: Mordacia mordax (anadromous), M. lapicida (anadromous), and M. praecox (resident and non-feeding). Similar to several Northern Hemisphere species, Southern Hemisphere species are targeted by fisheries (G. australis), culturally significant (to Māori and Mapuche), key prey for many species (including endangered species), and regarded as crucial links for understanding the evolution of vertebrates. Prior to this work, key information on the Southern Hemisphere lampreys was dispersed throughout the literature, hindering attempts to synthesise critical information about these species. Here we provide detailed descriptions of the five Southern Hemisphere species to facilitate the identification efforts by technicians, managers, researchers, and other interested parties. We then review the taxonomy, distribution, biology, genetics, significance, and threats to these lampreys from over 100 years of written sources (e.g., peer-reviewed publications and agency reports), complemented by interviews and Indigenous knowledge, in order to synthesise and centralise key information. We conclude by identifying Western science knowledge gaps and offering suggestions for addressing them: this is critical as anthropogenic environmental changes are negatively affecting Southern Hemisphere lampreys, and will likely continue to do so into the future.