Xiphosurans are aquatic chelicerates with a fossil record extending into the Early Ordovician and known from a total of 88 described species, four of which are extant. Known for their apparent morphological conservatism, for which they have gained notoriety as supposed ‘living fossils’, recent analyses have demonstrated xiphosurans to have an ecologically diverse evolutionary history, with several groups moving into non-marine environments and developing morphologies markedly different from those of the modern species. The combination of their long evolutionary and complex ecological history along with their paradoxical patterns of morphological stasis in some clades and experimentation among others has resulted in Xiphosura being of particular interest for macroevolutionary study. Phylogenetic analyses have shown the current taxonomic framework for Xiphosura—set out in theTreatise of Invertebrate Paleontologyin 1955—to be outdated and in need of revision, with several common genera such asPaleolimulusDunbar, 1923 andLimulitellaStørmer, 1952 acting as wastebasket taxa. Here, an expanded xiphosuran phylogeny is presented, comprising 58 xiphosuran species as part of a 158 taxon chelicerate matrix coded for 259 characters. Analysing the matrix under both Bayesian inference and parsimony optimisation criteria retrieves a concordant tree topology that forms the basis of a genus-level systematic revision of xiphosuran taxonomy. The generaEuproopsMeek, 1867,BelinurusKönig, 1820,Paleolimulus,Limulitella, andLimulusare demonstrated to be non-monophyletic and the previously synonymized generaKoenigiellaRaymond, 1944 andPrestwichianellaCockerell, 1905 are shown to be valid. In addition, nine new genera (Andersoniellagen. nov., Macrobelinurusgen. nov.,andParabelinurusgen. nov. in Belinurina;Norilimulusgen. nov. in Paleolimulidae;Batracholimulusgen. nov. andBoeotiaspisgen. nov. in Austrolimulidae; andAllolimulusgen. nov.,Keuperlimulusgen. nov., andVolanalimulusgen. nov. in Limulidae) are erected to accommodate xiphosuran species not encompassed by existing genera. One new species,Volanalimulus madagascarensisgen. et sp. nov., is also described. Three putative xiphosuran genera—ElleriaRaymond, 1944,ArcheolimulusChlupáč, 1963, andDrabovaspisChlupáč, 1963—are determined to be non-xiphosuran arthropods and as such are removed from Xiphosura. The priority ofBelinurusKönig, 1820 overBellinurusPictet, 1846 is also confirmed. This work is critical for facilitating the study of the xiphosuran fossil record and is the first step in resolving longstanding questions regarding the geographic distribution of the modern horseshoe crab species and whether they truly represent ‘living fossils’. Understanding the long evolutionary history of Xiphosura is vital for interpreting how the modern species may respond to environmental change and in guiding conservation efforts.