The Amu Darya (Persian: آمودریا‎, Āmūdaryā; Pashto: د آمو سيند, da Āmú Sínd; Arabic: جيحون‎, Jihôn or Jayhoun; Hebrew: גּוֹזָן‎, Gozan, Uzbek, Amudaryo, Greek: Ώξος, Oxus), also called Amu River, is a major river in Central Asia. It is formed by the junction of the Vakhsh and Panj rivers. In ancient times, the river was regarded as the boundary between Ariana (Afghanistan) and Tūrān.

In antiquity, the river was known by the Sanskrit name Vaksu, which now survives in Vakhsh, a tributary of the river.

In ancient Afghanistan, the river was also called Gozan, descriptions of which can be found in the book "The Kingdom of Afghanistan: a historical sketch By George Passman Tate".

In classical antiquity, the river was known as the Ōxus in Latin and Ὦξος Oxos in Greek — a clear derivative of Vakhsh — the name of the largest tributary of the river. In Middle Persian sources of the Sassanid period the river is known as Wehrōd (lit. "good river").

The name Amu is said to have come from the medieval city of Āmul, (later, Chahar Joy/Charjunow, and now known as Türkmenabat), in modern Turkmenistan, with Darya being the Persian word for "river".