Paratethys

thumb|right|alt=Palaeogeographical reorganization of the Tethys–Paratethys region during the Paleogene, from a connected Tethys configuration during the early Eocene (above) to a fragmented and restricted Paratethys region configuration during the Oligocene (below).|Palaeogeographical reorganization of the Tethys–Paratethys region during the Paleogene, from a connected Tethys configuration during the early [[Eocene (above) to a fragmented and restricted Paratethys region configuration during the Oligocene (below). Note the loss of deep-water connections between the Indian Ocean region and the Mediterranean, the complete loss of Indian–Arctic Ocean connections, and the closure of most of the Eocene seaways in the Oligocene time.]]

The Paratethys Sea, Paratethys Ocean, Paratethys realm or just Paratethys (meaning "beside Tethys"), was a large shallow inland sea that covered much of mainland Europe and parts of western Asia during the middle to late Cenozoic, from the late Paleogene to the late Neogene, and is regarded as the largest inland sea in history. At its greatest extent, it stretched from the region north of the Alps over Central Europe to the Aral Sea in Central Asia.