The Panj River (Persian: رودخانه پنج) (; Tajik: Панҷ, پنج), also known as Pyandzh River or Pyanj River (derived from its Russian name "Пяндж"), is a tributary of the Amu Darya. The river is 1,125 km long and forms a considerable part of the Afghanistan–Tajikistan border.
The river is formed by the confluence of the Pamir River and the Wakhan River near the village of Qalʿa-ye Panja (Qal`eh-ye Panjeh). From there, it flows westwards, forming the border of Afghanistan and Tajikistan. After passing the city of Khorog, capital of the Gorno-Badakhshan Autonomous Region of Tajikistan it receives water from one of its main tributaries, the Bartang River. It then turns towards the southwest, before joining the river Vakhsh and forming the greatest river of Central Asia, the Amudarya. Panj played an important role during Soviet times, and was a strategic river during the Soviet military operations in Afghanistan in the 1980s.