Saniwa is an extinct genus of monitor lizards that lived during the Eocene epoch around 48 million years ago. Well-preserved fossils have been found in the Bridger and Green River Formations of Wyoming, and evidence indicates Saniwa also lived in Europe. The type species S. ensidens was named in 1870 as the first fossil lizard known from North America. Several other species have since been added, but their validity is uncertain. It is a close relative of Varanus, the genus that includes extant monitor lizards.