The Olt River (Romanian and Hungarian; German: Alt; Latin: Aluta or Alutus) is a river in Romania. It is the longest river flowing exclusively through Romania. Its source is in the Hăşmaş Mountains of the eastern Carpathian Mountains, near the village Bălan. It flows through the Romanian counties Harghita, Covasna, Braşov, Sibiu, Vâlcea and Olt. The river was known as Alutus or Aluta in Roman antiquity. Olt County and the historical province of Oltenia are named after the river.

Sfântu Gheorghe, Râmnicu Vâlcea and Slatina are the main cities on the river Olt. The Olt flows into the Danube river near Turnu Măgurele.

The following towns and villages are situated along the river Olt, from source to mouth (incomplete list): Bălan, Sândominic, Miercurea Ciuc, Sfântu Gheorghe, Făgăraş, Brezoi, Călimăneşti, Râmnicu Vâlcea, Drăgăşani, Slatina, Drăgăneşti-Olt.

The following rivers are tributaries to the river Olt:

Olt may refer to:

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including stream, creek, brook, rivulet, tributary and rill. There are no official definitions for generic terms, such as river, as applied to geographic features, although in some countries or communities a stream may be defined by its size. Many names for small rivers are specific to geographic location; one example is "burn" in Scotland and northeast England. Sometimes a river is said to be larger than a creek, but this is not always the case, because of vagueness in the language.

Rivers are part of the hydrological cycle. Water within a river is generally collected from precipitation through a drainage basin from surface runoff and other sources such as groundwater recharge, springs, and the release of stored water in natural ice and snowpacks (e.g., from glaciers). Potamology is the scientific study of rivers.