Ichthyosaurus is a genus of ichthyosaurs from the Early Jurassic, with possible Late Triassic record, from Europe. It is among the best known ichthyosaur genera, as it is the type genus of the order Ichthyosauria.

Ichthyosauria is an order of large extinct marine reptiles sometimes referred to as "ichthyosaurs", although the term is also used for wider clades in which the order resides.