Protorosaurus is an extinct genus of reptile. Members of the genus lived during the late Permian period in what is now Germany and Great Britain. Once believed to have been an ancestor to lizards, Protorosaurus is now known to be one of the oldest and most primitive members of Archosauromorpha, the group that would eventually lead to archosaurs such as crocodilians and dinosaurs.

Archosauromorpha is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs rather than lepidosaurs. Archosauromorphs first appeared during the late Middle Permian or Late Permian, though they became much more common and diverse during the Triassic period.