Recent work on modern and fossil genera, and new approaches to classification, have rendered older classifications of lepidosaurs inadequate. This paper discusses the history of lepidosaurian classification from 1860 to the present, and then presents a new hypothesis of lepidosaurian relationships based on phylogenetic analysis. It offers a new definition of the Lepidosauria based on derived character states. Under this definition, squamates, sphenodontids and Gephyrosaurus are lepidosaurs; kuehneosaurs and younginiforms are not. The younginiforms are related to lepidosaurs and may be included within the Lepidosauromorpha. The taxonomic position of kuehneosaurs remains uncertain.