The origin of different names for Tethys is recounted, followed by a discussion of its geologic meaning. Much written recently is contrary to Suess's original ideas, which were based on good geologic data. Tethys is a paleogeographic feature not necessarily having paleozoogeographic overtones. It was a seaway, partly shallow, partly deep. At times it formed an enormous gulf on the east side of Pangea, and at other times it divided Gondwana from Eurasia. There were often islands in Tethys. Tethys came into being during the Cambrian or late Precambrian; it is not merely a feature that originated in Permian-Triassic time.