The Late Jurassic genus Pliosaurus was erected by Owen in 1841a. Since then numerous isolated bones and more complete skeletons have been referred to various species within the genus, many based on non-diagnostic material which has led to many uncertainties regarding the taxonomic status of Pliosaurus. Here, the species of Pliosaurus, their type and referred material are re-evaluated. Lack of distinctive type material demands selection of a neotype for P. macromerus (Philips, 1871) Lydekker, 1889a and a new neotype for P. brachyspondylus (Owen, 1839) Eichwald, 1868. Four species are recognised based on cranial tooth counts, cervical centrum morphology, retroarticular morphology, and relative propodial length. Three previously accepted named taxa are here considered invalid. This study is also the first to collectively illustrate an accurate stratigraphic provenance to, and what material is available from the main specimens referred to Pliosaurus. The results of this work form a foundation on which to build a more solid understanding of the diversity of this genus.