Transoxiana (also spelled Transoxania), known in Arabic and Persian sources as Mawarannahr (Arabic: "what (is) beyond the (Oxus) river"), is the ancient name used for the portion of Central Asia corresponding approximately with modern-day Uzbekistan, Tajikistan, southern Kyrgyzstan and southwest Kazakhstan.

Geographically, it is the region between the Amu Darya (Ancient Greek: Ώξος Ōxos) and Syr Darya rivers.

The area had been known to the Romans as Transoxania (Land beyond the Oxus), to the Arabs as Mawarannahr (Land Beyond the River), and to the Iranians as Turan, a term used in the Persian national epic Shahnameh.The region was one of the satrapies of the Achaemenid dynasty of Persia under the name Sogdiana.The name Transoxiana stuck in Western consciousness because of the exploits of Alexander the Great, who extended Greek culture into the region with his conquests of the fourth century BCE.

Transoxiana is the most northeastern point of the Hellenistic culture until the Arabic invasion.

During the Sassanid Empire, it is often called Sogdiana, a provincial name taken from the Achaemenid Empire, and used to distinguish it from nearby Bactria.